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Blood Sweat Tears and Grease => Projects => Restorations => Topic started by: SquidHunter on Jul 30, 2018, 13:09:12

Title: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 13:09:12
Iíve got an issue that I canít seem to put my finger on. After riding the bike for a while, and it warms up, it will sputter and die. It wonít start back up until the bike cools down. Iím thinking I might have a valve issue. Anyone experience this?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: 1fasgsxr on Jul 30, 2018, 13:25:38
My guess would be a fuel or fire issue. Im not familiar with the 750 ignition system but I would start there and carbs or petcock.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 15:36:42
My guess would be a fuel or fire issue. Im not familiar with the 750 ignition system but I would start there and carbs or petcock.

I upgraded the ignition, and charging system. Iíve completely cleaned and rebuilt the carbs, the right way. Plugs and wires and electrical wiring all new. Freshly sealed gas tank and new petcock...... but, the petcock is eBay. Iím suspicious of the petcock. I do get flow from it, but itís not a steady flow. Itís more like a chugging flow. Good then weak then good and weak again.

You really think that could be it? Seems like as long as the bowls stayed full it would be fine. Also, it will run fine until I get in traffic and the motor heats up. The valves seem to be in spec, but Iíve only checked when the motor was cold. Should I be checking with the motor warm?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 15:38:44
Also, it wonít start at all until after it cools down. Then it fires right up and seems to be fine


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 15:41:09
Same with a cold start. Fires straight away with choke up. Doesnít give me any problems until the motor gets hot.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: advCo on Jul 30, 2018, 16:05:17
Check your fuel cap and make sure the vent is clean and allowing air to flow. Sounds like the carbs are starving of fuel once they start trying to draw it down after riding for a few minutes. Once you the bike shuts off and cools, the  bowls will eventually fill back up and itll start up again.

Had the same exact issue on the XL350 with an aftermarket fuel cap.

I'd bet this is your problem.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 16:16:47
Check your fuel cap and make sure the vent is clean and allowing air to flow. Sounds like the carbs are starving of fuel once they start trying to draw it down after riding for a few minutes. Once you the bike shuts off and cools, the  bowls will eventually fill back up and itll start up again.

Had the same exact issue on the XL350 with an aftermarket fuel cap.

I'd bet this is your problem.

For sure not the fuel cap. I thought of this also. Pulled the cap and drilled a hole all the way through the top (it needs to be replaced anyway), just to check. Same issue. If itís starving for fuel, itís gotta be the petcock. The coils and ignition are all brand new. I just upgraded to an electronic ignition. Really strong spark.

The petcock they sent me is totally different than the stock, thatís why Iím betting on that. Especially seeing the fuel flow so erratically.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: advCo on Jul 30, 2018, 16:34:39
For sure not the fuel cap. I thought of this also. Pulled the cap and drilled a hole all the way through the top (it needs to be replaced anyway), just to check. Same issue. If itís starving for fuel, itís gotta be the petcock. The coils and ignition are all brand new. I just upgraded to an electronic ignition. Really strong spark.

The petcock they sent me is totally different than the stock, thatís why Iím betting on that. Especially seeing the fuel flow so erratically.


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Sounds like it, you should have steady flow out of the petcock or something is plugged up or not flowing correctly.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 18:50:35
Thanks for the replyís! This has me feeling much better. Iíll replace the petcock with a proper Honda unit


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: esmoojee on Jul 30, 2018, 19:40:49
Iíd say petcock, you should only check valves cold. Did you set the float height? That could affect it also. 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 30, 2018, 20:44:38
It's not valves, hard starting when cold but runs OK when hot is a sign of tight tappets on shim motors. (valve seats and faces wear faster than cam and shim so they get tight over time/mileage)The ignitors are the weak point on 750 and 900. Can't remember if they are visible from under seat or side panel but if you pull one off you may find melted potting compound? If you upgraded, what did you use? (GM ignitors?)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 22:07:17
Iíd say petcock, you should only check valves cold. Did you set the float height? That could affect it also.

Good. In that case they are in spec. Floats arenít adjustable on the 1980.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 30, 2018, 22:14:53
It's not valves, hard starting when cold but runs OK when hot is a sign of tight tappets on shim motors. (valve seats and faces wear faster than cam and shim so they get tight over time/mileage)The ignitors are the weak point on 750 and 900. Can't remember if they are visible from under seat or side panel but if you pull one off you may find melted potting compound? If you upgraded, what did you use? (GM ignitors?)

It starts every time, first bump, when cold. Itís craps out after riding for a while. Then it wonít start again until the motor cools down for at least 30 minutes or so.

No more ignitors. Iím using the power arc ignition, on the least aggressive timing curve.

I feel like my valves should be good because my compression is good across all four cylinders. Iím wondering if Iíve got one starting to stick when the motor heats up. The more I think about tho, the less that makes sense.

How about timing. Could heat relate to any timing issues?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 30, 2018, 23:01:49
Timing wouldn't make it cut out until it cools down.Do you have a timing light? If so, take it with you and connect up when it cuts out. no spark, found problem. It really sounds like ignition overheating and shutting down, just because it's new, doesn't mean it isn't faulty
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2018, 14:43:53
Timing wouldn't make it cut out until it cools down.Do you have a timing light? If so, take it with you and connect up when it cuts out. no spark, found problem. It really sounds like ignition overheating and shutting down, just because it's new, doesn't mean it isn't faulty

Thanks. Iíll try that. It does seem like an issue with heat. If the ignition is cutting out when it heats up, does that mean its faulty? Or is this a common issue with electronic ignition?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 31, 2018, 15:17:14
If ignition was designed for bike it would indicate it's faulty. If it's something adapted, it may just be in a position where it doesn't get enough airflow. Anything half decent will have a warranty.I'll have to look up Power Arc, never heard of it.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2018, 15:47:06
If ignition was designed for bike it would indicate it's faulty. If it's something adapted, it may just be in a position where it doesn't get enough airflow. Anything half decent will have a warranty.I'll have to look up Power Arc, never heard of it.

Itís an adaptation. Cycle X sells it


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2018, 16:00:55
If ignition was designed for bike it would indicate it's faulty. If it's something adapted, it may just be in a position where it doesn't get enough airflow. Anything half decent will have a warranty.I'll have to look up Power Arc, never heard of it.

Or perhaps the plugs are getting too hot 🤷🏻‍♂️. Iím running iridium plugs. Never had an issue before, but maybe switching to a colder plug would help


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 31, 2018, 17:43:56
Nope. Plugs overheating would cause pre-ignition, knocking and banging. possible piston damage.  Iridium plugs are best as a fit and forget, they don't need changing for 100,000 miles. Unless your doing high mileage touring they are most likely a waste of money in a bike. The 'best' I ever use are NGK platinum 'race' plugs. Are you using carbon plug leads or stranded copper wire? Carbon leads only last a couple of years before they need changing. When possible I always use stranded copper with silicon insulation but you must use correct resistance plug caps with them or you get wrong reverse EMF back to ignition control unit (in the 300vdc range on a 12v system) The iridium plugs will also have built in resistors, probably 4.5~5 K-Ohm so you need around another 5~7 K-Ohm in leads or caps 
Severely unimpressed with the Cycle-X ignition page. Any time you have to use a smaller plug gap it tells me ignition is a 'low' voltage unit (around 20,000v, probably less?.) Modern ignition system (even a multi spark) should be in the 35~50,000v range and use a wider gap. The other thing is, you must use carbon resistor leads? ? ?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2018, 20:23:25
Nope. Plugs overheating would cause pre-ignition, knocking and banging. possible piston damage.  Iridium plugs are best as a fit and forget, they don't need changing for 100,000 miles. Unless your doing high mileage touring they are most likely a waste of money in a bike. The 'best' I ever use are NGK platinum 'race' plugs. Are you using carbon plug leads or stranded copper wire? Carbon leads only last a couple of years before they need changing. When possible I always use stranded copper with silicon insulation but you must use correct resistance plug caps with them or you get wrong reverse EMF back to ignition control unit (in the 300vdc range on a 12v system) The iridium plugs will also have built in resistors, probably 4.5~5 K-Ohm so you need around another 5~7 K-Ohm in leads or caps 
Severely unimpressed with the Cycle-X ignition page. Any time you have to use a smaller plug gap it tells me ignition is a 'low' voltage unit (around 20,000v, probably less?.) Modern ignition system (even a multi spark) should be in the 35~50,000v range and use a wider gap. The other thing is, you must use carbon resistor leads? ? ?

Iím using what they sent me. Itís resistor plug caps for sure, and moroso wires. Seems to be high quality wires. I did gap the plugs at .22.

Thatís the only heat related problem I could find on power arcs website.

Still havenít had a chance to ride again, but next time Iíll pull the plugs and check for spark. It still has me scratching my head.

This is my first street bike, and definitely the first time Iíve dove into mechanics of a motorcycle. Iíve learned a lot, but I still feel like a total newb when something goes wrong. I appreciate the input.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 31, 2018, 20:48:06
I'm still kooking through Power Arc and Cycle-X (in between other stuff) I would say a wire has cracked or maybe circuit board and when things heat up the expansion is enough to create an open circuit. Honda had similar problem in 1978 where bikes would run when cold or over 4,000 rpm but if revs dropped they would not re-start. I have no idea how many bikes were recalled, it was a lot.
Hopefully your still within the 6 month warannty? PA website is pretty worthless, 'technical information' isn't. Basically it's an optical trigeer capacitor discharge system. Sounds real good and has a ton of adjustability / programmability, but, self contained units always have problems from heat and vibration. Optical sensors can also suffer from dirt/dust if not properly sealed (shouldn't be a problem on DOHC 750/900)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2018, 21:35:37
I'm still kooking through Power Arc and Cycle-X (in between other stuff) I would say a wire has cracked or maybe circuit board and when things heat up the expansion is enough to create an open circuit. Honda had similar problem in 1978 where bikes would run when cold or over 4,000 rpm but if revs dropped they would not re-start. I have no idea how many bikes were recalled, it was a lot.
Hopefully your still within the 6 month warannty? PA website is pretty worthless, 'technical information' isn't. Basically it's an optical trigeer capacitor discharge system. Sounds real good and has a ton of adjustability / programmability, but, self contained units always have problems from heat and vibration. Optical sensors can also suffer from dirt/dust if not properly sealed (shouldn't be a problem on DOHC 750/900)

I was just reading through it as well. I would place money on a wire losing voltage somewhere. Iíve got to rewire everything again anyway, so Iím sure Iíll find something there. I had to do a temporary job, to get it home. However, it should have been good enough to finish out the riding season. At least that was the hope.

Another theory is oil may be getting on the optical sensor. I did notice a drip from where the wire comes out. Thereís only one way that oil can get in, and I can fix that. Iíll have to ride it some more and recreate the problem. Hopefully itís not a faulty unit, but it should still be under warranty. If not..... lesson learned and on to the next.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Aug 01, 2018, 13:01:47
If I remember right there shouldn't be any oil in the ignition side of CB750DOHC (I haven't worked on them since 1980's) Even so, something disrupting optical sensor would be a 'permanent' problem and not something that only happens when hot.You can try cleaning trigger unit. I didn't see any mention of trigger type (IR, UV, red LED, visible, etc). You don't have any stress fractures from overtightened mounting screws? (PCB may have 'white' area's around screws)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 20, 2018, 15:13:15
I did get a chance to ride today. Swapped to a colder plug to no avail. Also, I checked the spark when I broke down. No spark. After letting it cool off for a minute, the bike fires up and runs fine


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: advCo on Aug 20, 2018, 16:12:21
I did get a chance to ride today. Swapped to a colder plug to no avail. Also, I checked the spark when I broke down. No spark. After letting it cool off for a minute, the bike fires up and runs fine


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Sounds like you need to get some new coils. Have you checked the primary and secondary resistances on your coils?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: J-Rod10 on Aug 20, 2018, 17:45:07
If I remember right there shouldn't be any oil in the ignition side of CB750DOHC (I haven't worked on them since 1980's) Even so, something disrupting optical sensor would be a 'permanent' problem and not something that only happens when hot.You can try cleaning trigger unit. I didn't see any mention of trigger type (IR, UV, red LED, visible, etc). You don't have any stress fractures from overtightened mounting screws? (PCB may have 'white' area's around screws)

There is oil in the ignition side of the DOHC. Timing cover has an o-ring to keep it in there.

If you pop that cover off while on the sidestand, you're going to have a mess in your floor.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Aug 20, 2018, 18:41:15
Sounds like you need to get some new coils. Have you checked the primary and secondary resistances on your coils?
As it's heat related you would need to 'cook' them up to temp before checking as cold/room temp readings may be OK
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 20, 2018, 19:15:35
There is oil in the ignition side of the DOHC. Timing cover has an o-ring to keep it in there.

If you pop that cover off while on the sidestand, you're going to have a mess in your floor.

It does for sure. Not a lot, but enough to make a mess.

I just got off the phone with Gary from power arc, and then Ken from Cycle X. 🤦‍♂️

Ken says I should go back to a lead acid battery. Gary says Kens charging system is the blame. Apparently it uses a ďshuntingĒ ground regulator, so while Iím running high rpms the excessive charge is over shunting and building up heat. The ignition has a built in safety feature that shuts it down with excessive voltage/heat. 🤷🏻‍♂️

Gary is supposed to send me a link from a study that was done. Apparently there was a similar issue with an aprillia race bike......

So, in the meantime Iíve got about 1500 bucks tied up in some shit that donít work....... or does, too good


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 21, 2018, 00:08:13
As it's heat related you would need to 'cook' them up to temp before checking as cold/room temp readings may be OK

So I got the link. Apparently the problem is related to the charging system Iím using from Cycle X. The regulator is a ďshuntĒ r/r, and itís shunting excessive voltage in the high rpms. This is causing the motor to run about 20 degrees hotter than normal. Supposedly a series regulator/rectifier would be the fix. Itís 175 bucks!

The ignition and charging system are both working as they should, but apparently they arenít a good match on my bike. The excessive heat is triggering a safety mechanism, built in, to prevent a meltdown. Once it cools off itís back to business.

This presents a problem.....

Looks like itís time for a new bike


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Aug 21, 2018, 16:19:37
The charging system on CB750/900 DOHC shouldn't be using a shunt, it's supposed to 'switch off' voltage to field coils. Shunt is used on permanent magnet systems as magnetic field can't be 'switched off' or varied. Either way, it shouldn't cause motor to run 20 deg hotter
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 21, 2018, 21:18:20
The charging system on CB750/900 DOHC shouldn't be using a shunt, it's supposed to 'switch off' voltage to field coils. Shunt is used on permanent magnet systems as magnetic field can't be 'switched off' or varied. Either way, it shouldn't cause motor to run 20 deg hotter

Iím running Cycle Xís charging system. Itís the same as a Norton. Itís a shunt R/R. Apparently itís fine until the battery is fully charged and the rpms are high. Itís running hotter for sure.

Worst case scenario, Iíll just go back to stock.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: themotoworks on Aug 21, 2018, 21:22:41
I've had this problem on a few bikes, take a look at the plugs when it craps out.  I had one running so rich at one range that if I was in traffic running in that range long enough, it would start losing idle, only run when the throttle was over 1/4 open, and eventually die alltogether, let it cool down completely, it would fire back up.  once I realized what was going on, I retuned it and got it a lot leaner on idle and just a bit above, ran fine afterwards
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 21, 2018, 22:00:17
I've had this problem on a few bikes, take a look at the plugs when it craps out.  I had one running so rich at one range that if I was in traffic running in that range long enough, it would start losing idle, only run when the throttle was over 1/4 open, and eventually die alltogether, let it cool down completely, it would fire back up.  once I realized what was going on, I retuned it and got it a lot leaner on idle and just a bit above, ran fine afterwards

When I originally wired up the ignition system, I was running way too rich. I ended up going back to the stock jetting, because it fouled my plugs.

Iíve pulled the plugs when it happens, and if anything they are showing lean. The problem is they arenít getting spark. After it cools down Iíve got plenty of spark. Itís a safety mechanism thatís being tripped in the ignition.

Hereís a copy of the link that power arc sent me. Itís pretty interesting
http://www.bayarearidersforum.com/forums/showthread.php?t=394141&page=4



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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 27, 2018, 23:23:26
Spoke with Ken at Cycle X today. Super solid guy. Heís going to ship me a series R/R. If that doesnít fix it, then we will know without a doubt itís the ignition.

The theory, according to Power arc, is this will cool down the charging system. Hence cooling down the motor. Weíll know within about a half hour of riding when it arrives. Fingers crossed


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: VintageMBike on Aug 31, 2018, 21:58:20
Spoke with Ken at Cycle X today. Super solid guy. Heís going to ship me a series R/R. If that doesnít fix it, then we will know without a doubt itís the ignition.

The theory, according to Power arc, is this will cool down the charging system. Hence cooling down the motor. Weíll know within about a half hour of riding when it arrives. Fingers crossed


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I bought that same Cycle X setup for my 82 Honda cb 900F (after reading one of your posts in this forum). No offense to the nice guys at cycle x, but the advertising was misleading: NEW POWERFUL HONDA CHARGING SYSTEM WE DEVELOPED" when it was really Norton Brit Bike technology.

I havent had any issues with the Cycle X charging system, and I know 900f's run a bit hot anyway, but time will tell. Fingers crossed I dont have any issues.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Aug 31, 2018, 22:27:53
I bought that same Cycle X setup for my 82 Honda cb 900F (after reading one of your posts in this forum). No offense to the nice guys at cycle x, but the advertising was misleading: NEW POWERFUL HONDA CHARGING SYSTEM WE DEVELOPED" when it was really Norton Brit Bike technology.

I don't see where you got your quote from on their DOHC charging system page, but they can still say they developed the system for the DOHC Hondas even if they are using "Norton Brit Bike technology."  The Wassell part of the equation is the way they encase the windings, not in the technology.  If we want to get technical, they are using Hippolyte Pixii technology.  Regardless, according to your quote, they say they "developed" the system, not "invented" or "patented" the system.  Developing technology is when you take existing tech and adapt it , ie. make them for Hondas. 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Sep 01, 2018, 00:45:36
I didn't know he was the one who invented the permanent magnet alternating current generating system.  Learn something new every day.

Isn't it just a Lucas RM23 (or whatever the model number is) that we were fitting to our Trumpets and Beezas all those years ago?  Admittedly I would never have though of fitting one to a Honda, but maybe I lack imagination.

Lucas used to dump surplus power as heat through a single Zener diode with a big heat sink. I'm guessing that's what they still do in maybe a more sophisticated package of some sort.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: kopcicle on Sep 01, 2018, 01:54:45
fsck'n Honda iggy bits
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Sep 02, 2018, 21:24:25
fsck'n Honda iggy bits
You've probably seen hundreds with the guts melted out, I know I've seen a few dozen
I didn't know he was the one who invented the permanent magnet alternating current generating system.  Learn something new every day.

Isn't it just a Lucas RM23 (or whatever the model number is) that we were fitting to our Trumpets and Beezas all those years ago?  Admittedly I would never have though of fitting one to a Honda, but maybe I lack imagination.

Lucas used to dump surplus power as heat through a single Zener diode with a big heat sink. I'm guessing that's what they still do in maybe a more sophisticated package of some sort.
   

 Didn't Tesla invent AC generator? I wouldn't think of fitting an old LUCAS system on CB900 either. I doubt it's something 'clever', probably still a zener diode but without the heatsink?. I never had any real issues with zeners, vibration always broke the terminal pin before they burned out or did anything nasty which totally sucked as the zener was always fine but impossible to get a wire back on 99% of time
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Sep 02, 2018, 21:49:43
You've probably seen hundreds with the guts melted out, I know I've seen a few dozen   

 Didn't Tesla invent AC generator?
No, Hippolyte Pixii did in 1832, more than 30 years before Tesla was even born.

(https://upload.wikimedia.org/wikipedia/commons/5/56/Wechselstromerzeuger.jpg)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: datadavid on Sep 03, 2018, 07:31:51
Didnt tesla prefer high voltage dc?
No, Hippolyte Pixii did in 1832, more than 30 years before Tesla was even born.

(https://upload.wikimedia.org/wikipedia/commons/5/56/Wechselstromerzeuger.jpg)

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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Sep 03, 2018, 09:42:46
Didnt tesla prefer high voltage dc?
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No, Edison did.  In the War of the Currents, Tesla presented AC power and Edison presented DC.  At the time, there wasn't a way to deal with power loss for DC, but Tesla had invented an AC transformer, so AC power won out. 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: datadavid on Sep 03, 2018, 09:52:31
No, Edison did.  In the War of the Currents, Tesla presented AC power and Edison presented DC.  At the time, there wasn't a way to deal with power loss for DC, but Tesla had invented an AC transformer, so AC power won out.
Cool, i know way too little about this stuff.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Sep 03, 2018, 20:32:33
Thanks for the history lesson irk.  8)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Sep 03, 2018, 21:28:40
Haha.  The cool thing about it all, and sorry for all of this thread jacking, is nowadays with wind power and solar power the technology has finally caught up to what Edison was trying to do.  It's amazing to think how much he was ahead of his time. 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 03, 2018, 23:30:48
So apparently the heat issue will be solved by adding a series regulator.  About to test the theory. Ken is sending me one. My bike is running too hot for the ignition to function properly. Everything runs great unless I hit a few redlights.

This is based on information supplied by Gary from power arc, however. It could be power arc trying to pass the buck, but the science made sense so here goes nothing.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 13, 2018, 20:37:31
So the series regulator came Wednesday. Let me be the first to say, itís gigantic and weighs about 4lbs. Wired it up today. Did not solve the heat issue. Did not solve the ignition issue.
I called Ken at Cycle X. Heís had been thinking about the issue a lot, and suggested that I wire the regulator straight to the battery, thinking it may be a noise issue.
I did, and I think it worked 🤷🏻‍♂️. Took the bike for a romp through the city. Plenty of rpms, and plenty of redlights. No breakdown since. Iím going to take it on a longer ride Sunday to be for sure.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 13, 2018, 21:25:47
Question: what size fuse should I use to run the regulator straight to the battery?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Sep 14, 2018, 07:46:42
I wouldn't run a fuse between the regulator and battery, but I'd run them between the battery and everything else.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Sep 14, 2018, 12:00:02
Yep, do as Irk says. Running a fuse between regulator and battery will cause a 'runaway' condition if it breaks and fry everything electrical. (you'll have at least 17v but more likely 90+@5,000rpm)
With battery in circuit, the reg has a reference voltage.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: kopcicle on Sep 14, 2018, 12:39:50
one more time for those that were not paying attention ...


replace the igniter(s) and or pickups until it works
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Sep 14, 2018, 12:43:38
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 14, 2018, 22:35:58
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.

Iím in Birmingham Alabama. The air temperature is hot. 80-90 degrees. Iím running a slight touch lean, Iím almost certain. There was a setback, and I havenít put it on a dyno yet. I wanted to dyno it, and jet from there. However, Iím still running the stock airbox/filter.

The series regulator was supposed to cause less stress on the charging system. Thereís some thermal imaging of bikes running with and without, and apparently it causes them to also run cooler 🤷🏻‍♂️. But, nasa isnít knocking down my door for electrical advice.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 14, 2018, 22:38:05
one more time for those that were not paying attention ...


replace the igniter(s) and or pickups until it works

Thereís no igniters and no pickups. The ignition is power arc.

Noise interference is the issue Iím having


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 14, 2018, 22:45:40
I wouldn't run a fuse between the regulator and battery, but I'd run them between the battery and everything else.

Well, incidentally, this is how itís now wired. My plan is to get it running right, then break everything down so I can build it right. Iíve got to weld some mounting tabs, and paint the frame and tank/side covers. Suspension etc etc...

So Iíve done a ďtemporaryĒ harness to sort it out. I wanted to start from nothing, and figure it out. Canít even tell you how much Iíve learned.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 14, 2018, 22:52:36
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.

The original theory was that engine temperature was tripping a safety mechanism in the ignition. Itís built in to prevent a ďmeltdownĒ.......supposedly. Turns out, itís probably a noise issue due to the regulator being wired to the starter solenoid (ie: like ďstockĒ). Wiring the regulator strait to the battery solves that....apparently 🤷🏻‍♂️

All new information to me, and most of the technical is over my head. But if it works, Iím in.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Sep 14, 2018, 23:33:00
Too many noisy electrons will create issues.  Not sure about the wiring change though.  Battery to starter and wire from that same terminal to the regulator. How does that differ from a wire direct from the battery to the regulator? And what is the noise source?  I don't know about electrical issues to pass judgement - just trying to understand and clear the smoke to see what is actually happening.

I get that the ignition might have some sort of thermal overload protection but it made no sense that the charging circuit was a cause of overheating.  Good to see that theory has been taken off the table.  Keeping in mind that I wouldn't know an electron if I ran it over, I wonder if that new alternator might be generating waves (ripples) in the DC circuits that caused the ignition to freak out.  Maybe the new regulator acts as a smoothing device in some way.

BTW, most bikes now seem to have a 30 amp fuse built into the starter solenoid wiring between the battery and everything else. If it blows, all power to all circuits is cut, so no more engine generating power, so I'd guess that is not an issue. 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Sep 14, 2018, 23:37:57
One advantage to running a fuse per individual circuit vs. a breaker for the whole harness is being able to isolate an issue easier.  If my headlight fuse blows, I know where to look because the fuse told me.  If a circuit breaker blows, I'm checking the whole harness hoping I don't test the headlight circuit last.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 15, 2018, 21:58:24
Too many noisy electrons will create issues.  Not sure about the wiring change though.  Battery to starter and wire from that same terminal to the regulator. How does that differ from a wire direct from the battery to the regulator? And what is the noise source?  I don't know about electrical issues to pass judgement - just trying to understand and clear the smoke to see what is actually happening.

I get that the ignition might have some sort of thermal overload protection but it made no sense that the charging circuit was a cause of overheating.  Good to see that theory has been taken off the table.  Keeping in mind that I wouldn't know an electron if I ran it over, I wonder if that new alternator might be generating waves (ripples) in the DC circuits that caused the ignition to freak out.  Maybe the new regulator acts as a smoothing device in some way.

BTW, most bikes now seem to have a 30 amp fuse built into the starter solenoid wiring between the battery and everything else. If it blows, all power to all circuits is cut, so no more engine generating power, so I'd guess that is not an issue.

My solenoid has a 30amp fuse. My original thinking was that this would be great, considering the stock harness plugs in at the solenoid. But, the stock ignition isnít effected by noise.

Apparently both regulators are producing noise. But, wiring it straight to the battery eliminates that noise 🤷🏻‍♂️. This is the first time Iíve heard this, but......

Tomorrow Iíve got some guys together, and weíre going to shred the surrounding area. Iíll know for sure if itís fixed tomorrow. No holding back


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 15, 2018, 22:03:39
One advantage to running a fuse per individual circuit vs. a breaker for the whole harness is being able to isolate an issue easier.  If my headlight fuse blows, I know where to look because the fuse told me.  If a circuit breaker blows, I'm checking the whole harness hoping I don't test the headlight circuit last.

You are exactly right. My plan is to run a m-unit. Just trying to work out the bugs for now.

If my headlight fuse blows, my fuse is my headlight.....

Iím going to run LEDS and all that, so Iím not particularly worried about it at this time. Iíve blown that 30amp solenoid fuse about 5 times messing with the electrical. When I say messing, I mean just that. Itís been a total mess. As I expected, Iím walking away with a ton more knowledge though.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 16, 2018, 16:51:12
Ok. Rode the bike today for about 5-6 hours. Hereís what I found out. With the ignition cover on, it will break down. With it off, it will run perfect indefinitely. This leads me to believe itís a heat issue and not a noise issue. The bike isnít any hotter than it would normally be. It is an oil cooled bike, but I still feel like itís a faulty ignition module.

I rode today, all day, with the cover off but thatís not a good permanent solution


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 17, 2018, 23:31:46
Seriously considering just drilling out the cover.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Sep 18, 2018, 00:22:55
Isn't it an optical system which would tend to have issues if it's not covered or at least shielded from ambient light?  Maybe drill holes to improve air flow in a way that keeps out the light.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 18, 2018, 09:30:03
Isn't it an optical system which would tend to have issues if it's not covered or at least shielded from ambient light?  Maybe drill holes to improve air flow in a way that keeps out the light.

Itís an optical sensor. Seems to be similar to an abs sensor, like on a ktm duke. Ambient light doesnít seem to effect it.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: Pete12 on Sep 18, 2018, 09:42:04
Isn't it an optical system which would tend to have issues if it's not covered or at least shielded from ambient light?  Maybe drill holes to improve air flow in a way that keeps out the light.
Optical sensors generally use infrared technology which is unaffected by ambient light
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Sep 18, 2018, 10:53:43
That's interesting.  Lumenition and Newtronics both say to keep them covered up and people have all sorts of horror stories about Newtronics and ambient light.  Maybe because ambient includes the whole range of light from red to blue.

I'm no light engineer.  Just passing on what I have read.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 19, 2018, 08:57:37
Now they are sending me a diode to wire in. This is supposed to eliminate all noise possibilities. If that doesnít work, then weíll see what happens I guess. Gary at power arc seems to be in denial that there could be a problem with the ignition.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Sep 24, 2018, 21:57:06
It came today. I would be surprised if this made a difference


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 07, 2018, 22:18:28
The diode didnít work. I spliced it in today, and the bike still breaks down with the ignition cover on. Take the cover off, and no problems at all


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 08, 2018, 16:07:37
Hereís my next test. Since the bike runs with the cover off, my theory is itís a heat problem. Iíve drilled out a cover I had laying around


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Oct 08, 2018, 21:00:54
Time to buy a nice simple DYNA S  and see how that goes. 

BTW. how hot is the ignition when it fails?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 08, 2018, 22:04:23
Time to buy a nice simple DYNA S  and see how that goes. 

BTW. how hot is the ignition when it fails?

I may end up doing just that. I havenít taken a temperature reading, but itís not any hotter than the motor would typically get. I live in the city, so traffic and redlights are the norm.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 09, 2018, 14:02:30
Looks like seller of ignition thought it may be power spike although I don't see how a bridge rectifier would help.  If he actually developed ignition *and isn't just marketing something) I would have thought a simple diode bridge and capacitors would work better. It's more than likely one of the 'Military Spec' components  is either breaking down or simple turning off when it heats up. Manufacturer should eb doing more to help you out, so far it's a good advertisement to avoid them at all costs
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 09, 2018, 21:37:54
Looks like seller of ignition thought it may be power spike although I don't see how a bridge rectifier would help.  If he actually developed ignition *and isn't just marketing something) I would have thought a simple diode bridge and capacitors would work better. It's more than likely one of the 'Military Spec' components  is either breaking down or simple turning off when it heats up. Manufacturer should eb doing more to help you out, so far it's a good advertisement to avoid them at all costs

You hit the nail on the head. The diode was the last effort to eliminate electrical issues. THE WHOLE TIME Iíve been saying itís a heat issue with the ignition. Itís very obvious. The problem is power arc doesnít want to admit thereís something wrong. Ken at cycle x has been the one trying to figure it out. Now itís been drawn out long enough the warranty is no good, so Iím basically screwed out of 600 bucks. Iím over all the back and forth. I just want it to run right. I need dependability over performance, because Iíll be traveling on this bike. I have been traveling on this bike.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Oct 09, 2018, 21:46:52
For dependability, I'd go back to the original Honda system.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 09, 2018, 22:40:13
For dependability, I'd go back to the original Honda system.

I could do that, but itís hard to believe that nobody has designed anything better. The erratic behavior of the stock ignition, paired with the stock charging system is nerve racking. My stock charging system failed three times since Iíve owned the bike. I went to the cycle x charging system, then my stock ignition failed (whilst riding 600 miles from home). Then I went to the power arc ignition from cycle x, and I havenít been able to achieve reliability since.

The bike runs great, until it breaks down. Iíll check the spark. No spark. Take the ignition cover off..... boom, instant spark. I can ride all day and night with the cover off.

Ken at cycle x tells me heís got one in the shop with the same set up, and he canít even make it fail. I believe him. I just donít know whatís different on his bike than mine. I have to believe itís a difference in the wiring, or perhaps because Iím running an agm battery?

Iíve got to pull everything apart anyway, so Iím thinking I may try wiring the coils straight to the battery, instead of through the ignition switch. I read through some information that suggested that. Apparently the ignition module shuts the coils off with the kill switch, and it isnít necessary to run them through the switch. Power arc even suggests this, due to fluctuations in voltage through the switch. That still doesnít explain why it runs great with the cover off however.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 09, 2018, 23:36:17
Haven't read all your post yet so may amend this. There is nothing bad about stock ignition system as long as bike is running. It does have problem when ignition is left on and engine isn't running, ignitors overheat pretty quick as they never had a timer or shut off. I would probably get the trigger units and use any of the aftermarket boxes. (even GM can be used at about $20.00 each and about $50.00 for 'high temp' versions) Only time I've seen issue with stock charging systems is when they are used to charge 'dead' batteries.(even brand new ones that were not prepped properly) The charging system can put out about 20 amps but only for very very short period. If the regulator /rectifier tries to maintain high output the internal regulator burns out then the diodes start overheating and often short circuit. Battery goes flat and new battery gets fitted which discharges through charging coils burning off the insulation. A battery will fail if left discharged (10v or less) for about 30 days. You need to get back on Power-X and get them to test ignition at 220f (then get them to replace it when they say it's 'fine') I would also make a lot of noise on their Facebook site (pretty sure they will have one, 'they all' like free advertising) Itonly took 48 hrs for Yahoo to fix my problem when I was locked out, other people had been complaining for 3~4 months and getting run-around with automatic replies I guess negative results on Facebook do carry some weight?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Oct 10, 2018, 15:06:55
The voltage regulators in old 50's, 60's cars were electro-mechanical relay type (many had adjustable voltage control), and often lasted for several decades. It's hard to understand why solid state devices can't hold up as well. All they have to do is sense the voltage and turn the field current on/off to maintain it. The diodes in the rectifier could always be uprated.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 10, 2018, 23:05:55
Iím generally good with mechanics. I understand motors, and I work meticulously. Electrical on the other hand...... blows my mind every time. Especially the technical side of it. Absolutely a pain in my ass. This is the main reason Iíve stripped everything off my bike and made it as simple as possible. Thatís also the reason Iíve chosen the components I have. Simple.

Iím still suspicious the battery Iíve chosen may be the root of my problems. Reason being, these components were designed to work with a lead acid battery. I chose a agm battery (for the warranty, mainly), and didnít really do the homework before hand.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: VintageMBike on Oct 11, 2018, 18:18:20

I think you and i conversed about this. I have a 900f pictured below.

When I first bought it, batteries kept dying, all sorts of shit.

I bought the Cycle X 3 phase thingy (its really a brit charging system) installed it myself with a new battery, and havent had a problem since (well, the battery DID die thereafter when I had to ride 2 up with a friend whose bike broke down in the dead of night. With my headlight on and the extra load, it died just as we got where we needed to go. I ran it a while after with the headlight off and it was fine).

There maybe be an issue in your particular bike that is causing this.

\
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 11, 2018, 20:46:47
I
Iím still suspicious the battery Iíve chosen may be the root of my problems. Reason being, these components were designed to work with a lead acid battery. I chose a agm battery (for the warranty, mainly), and didnít really do the homework before hand.

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AGM is still lead acid its just the acid is Absorbed by a Glass Mat (the acid is slightly higher specifig gravity, 1.32 instead of 1.27) As long as you don't go lower than OEM A/Hr it will be fine. AGM batteries are smaller and higher output due to the mat, plates can be closer together and use stronger acid. If you fit a 6~8 A/Hr battery instead of ~14 A/Hr it will 'boil dry' within a short time. It's possible (pretty easy) to remove top cap/strip and check it's still wet. You shouldn't have fluid showing but separators should be wet. Personally I've always had to add some de-ionised water to every one I've had. Even though they are 'sealed' there is an over pressure vent to stop them exploding if over charged
VintageMBike, I'll bet your 900 runs real good wirth the CR carbs?

Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 11, 2018, 21:01:16
To be clear, I donít have a charging problem. The cycle x charging system solves that. Iíve got an ignition problem


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 12, 2018, 17:48:51
Just pointing out AGM battery won't be a problem. As for ignition, I guess you'll have to harrass them as much as possible to get anything done. I would say they know there is a problem but messed you about until warantee expired? Wouldn't be the first company to do that.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Oct 12, 2018, 18:12:36
You just said something interesting.  You said that it dies but when you remove the cover, it fires back up.  If the bike had been a twin I would have said to check the points wires to see where they touch the cover.  Yours is a very different animal but I wonder if there is something else going on here. I know you said that it starts up OK with cover on but dies after a certain amount of time, so it cannot just be a simple short but is there any way that as it gets hot, that a wire might touch the outer cover?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 12, 2018, 21:34:33
You just said something interesting.  You said that it dies but when you remove the cover, it fires back up.  If the bike had been a twin I would have said to check the points wires to see where they touch the cover.  Yours is a very different animal but I wonder if there is something else going on here. I know you said that it starts up OK with cover on but dies after a certain amount of time, so it cannot just be a simple short but is there any way that as it gets hot, that a wire might touch the outer cover?

That is an interesting thought. Iíve got too much going on this weekend, but over the next couple of weeks Iíll be digging in. Thereís only one set of wires routed out, and not many. The wires are individuals insulated, then I have them all wrapped together in tape like a small harness. There could be something to that though.

The problem with riding with the cover off, is light effects the optical sensor. I rode to work today, and it ran like garbage. Didnít break down, because the cover was off, but it was erratic behavior for sure. It even seems like itís running rich now. Doesnít make any sense. Still running the airbox and stock jet sizes. I know itís the ignition.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 12, 2018, 21:38:12
Just pointing out AGM battery won't be a problem. As for ignition, I guess you'll have to harrass them as much as possible to get anything done. I would say they know there is a problem but messed you about until warantee expired? Wouldn't be the first company to do that.

See, thatís what I thought too. Iím just fishing for opinions. I havenít had any problems with the agm battery. Iíve been running it for 6 months without any battery/charging issues. Iím definitely having ignition issues.

I


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: advCo on Oct 17, 2018, 09:26:21
Go back to stock?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 17, 2018, 15:33:55
You just said something interesting.  You said that it dies but when you remove the cover, it fires back up.  If the bike had been a twin I would have said to check the points wires to see where they touch the cover.  Yours is a very different animal but I wonder if there is something else going on here. I know you said that it starts up OK with cover on but dies after a certain amount of time, so it cannot just be a simple short but is there any way that as it gets hot, that a wire might touch the outer cover?
This reminded me of something that happened around 1978~79. I did an accident repair and had intermittent fault. The outer sheath of ignition wires had been crushed but showed good continuity when checked. I  was getting a miss-fire about 20 mins after startup so assumed it was carb/fuel flow fault. Anyway, after a bunch of messing around, turns out wires were broken inside insulation.
I found it by 'stretching' wires after cutting off outer sheath. I also had a GS1000 where the bullet connectors were slightly loose and had a miss when hot. It would be unlikely but at least you'll know what it isn't, further ammuniotion when arguing about faulty ignition system
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 17, 2018, 22:28:35
This reminded me of something that happened around 1978~79. I did an accident repair and had intermittent fault. The outer sheath of ignition wires had been crushed but showed good continuity when checked. I  was getting a miss-fire about 20 mins after startup so assumed it was carb/fuel flow fault. Anyway, after a bunch of messing around, turns out wires were broken inside insulation.
I found it by 'stretching' wires after cutting off outer sheath. I also had a GS1000 where the bullet connectors were slightly loose and had a miss when hot. It would be unlikely but at least you'll know what it isn't, further ammuniotion when arguing about faulty ignition system

Now youíve really got me thinking. The one thing that Iíve assumed is my wiring was good, due to the fact that itís so simple. Iíve got to rewire it anyway, so I might as well pull it all apart and have a look-see.

What is everyoneís recommendations on wiring a bike? Iíve got good tools for crimping and stripping, so I havenít been soldering my connections. Some say thatís fine, but my chopper friends say solder everything. After this experience, Iím thinking solder as much as possible and use less connectors. For example, solder and heat shrink as opposed to bullet connectors.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 17, 2018, 22:33:39
Go back to stock?
I can go back to stock. But, when my bike is running good, I get a taste of the good life. I want that consistently.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Oct 18, 2018, 07:41:59
On the machines (sold for around $1.25 M each) I used to work on, we were getting some strange intermitent electrical issues on random circuits. Turned out one of our vendors was using the wrong stripper/crimper combo. They were crimping on the insulation with random contact of the wire to the connector inside the pins. Bugger to chase down. We also cooked some good sized breakers where they had not stripped cables far enough and tightened lug down partially on the insulation. Made contact until real current was drawn through it, then started heating up. So many things can go wrong in wiring. Particularly in connections that rely on compression for current flow.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 18, 2018, 18:29:16
Now youíve really got me thinking. The one thing that Iíve assumed is my wiring was good, due to the fact that itís so simple. Iíve got to rewire it anyway, so I might as well pull it all apart and have a look-see.

What is everyoneís recommendations on wiring a bike? Iíve got good tools for crimping and stripping, so I havenít been soldering my connections. Some say thatís fine, but my chopper friends say solder everything. After this experience, Iím thinking solder as much as possible and use less connectors. For example, solder and heat shrink as opposed to bullet connectors.


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Although I've used both (and still do) solder connections can fail due to vibration quicker than crimp connections. As long as wires are clean and crimped properly they are not an issue (plenty of 40+ ye old bikes still running original connectors)  It's easy enough to do a continuity check when bike is hot and cuts out  if removing cover 'cures' problem I would look specifically at the wires from trigger units to control box/coils. Also, check wire routing, I've seen cable clips bent so tight they cut wires and also (again on GS1000) wiring not in clips melted onto exhaust pipe but it only cut out above 80mph when airflow pushed wires onto pipe. At least that wasn't as bad as the GSX cutting out aat sustained 155mph., we ended up giving it back to Suzuki to fix
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 18, 2018, 21:10:27
Thereís a very important lesson here. Thanks a lot


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 28, 2018, 20:12:15
Rode my bike some today. Completely frustrated with the ride, I came home and started digging into the wiring. Sure enough, I had a loose connection. It was the white wire that signals the work coil. Makes sense now.

I should have taken some photos. Ive got the day off tomorrow, so Iím going to attempt to complete the rewire. Iím going to change a few things. 1. Iím going to wire the coils straight to the battery 2. Iím going to wire the regulator/rectifier straight to the battery 3. Iím going to use the least amount of connectors possible


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 29, 2018, 00:15:50
If you wire coils direct to battery will you be able to turn them off? Easy fix would be use a relay to get full voltage to coils. I had to do similar on my Katana as it's a known fault that causes overcharging (low voltage to regulator gets 17+volt charge and causes battery to boil dry)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: J-Rod10 on Oct 29, 2018, 00:51:15
Fused relay is what you want.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 29, 2018, 19:43:47
Iíve got a fused relay that I was running on my stock coils, to bypass the ignition switch. According to power arc this isnít necessary with their system. The control module turns them on and off 🤷🏻‍♂️. Thatís what they say anyway.

Iím super bummed out. I was supposed to work on it all day today, but got called into work. sigh....


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 29, 2018, 22:04:04
Always seems to happen. Either you have time but no money or money but no time. Since looking after grandson I have neither time or money (at least none to do things I want  ;D )
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Oct 31, 2018, 00:04:16
Always seems to happen. Either you have time but no money or money but no time. Since looking after grandson I have neither time or money (at least none to do things I want  ;D )

I bet grandkids are rad tho. Iíve got a 4 yo son. Itís pretty fun, but grandkids seem more fun


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Oct 31, 2018, 12:43:05
I've been looking after him for 2yrs, he was 3 couple of weeks ago.Much harder work than I expected but mostly great fun. Here is is this morning and a couple of days ago before haircut with Nana's sunglasses  ;D   Kinda surprised how well the 10 yr old 'Kid Tough' camera works, his cousin had it when she was about same age (she's 15 now) 
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 06, 2019, 21:13:57
Ok guys, long time no update. I finally bit the bullet and buckled down on the Honda. Completely reworked the wiring. Took my time and did it right. Soldered all the connections and everything. Bike fires up first try and rides amazing. Hereís the kicker: same exact problem! After the motor gets good and heat soaked, the ignition fails and Iím getting no spark. After it cools down, fires back up and runs good. Iíve been riding with a laser thermostat in my pocket because of this. It seems to fail when the ignition model reaches 145 degrees. Then restarts when it cools down by 20 degrees.

I called Gary at power arc, and explained the situation. Iíve literally tried everything from diodes, colder plugs, even a 200 dollar mosfet regulator. Always the same problem, and even weak spark on cylinder one most of the time.

Today I shipped it to him for further testing. He says he can make it right. So far Iím super disappointed with the whole situation. Iíve spent almost as much on this as I paid for the bike


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jun 06, 2019, 21:30:00
There is something wrong with that ignition. 145f is pretty hot but if built properly it should still be working. If it's got a thermal overload cut out  it's set wrong I guess. There has to be a reason it's getting warm though, 120f isn't particularly hot for most motorcycle (or automotive) components inside engine bay area. I used non contact thermometer on the tarmac out side the house last week. Air temp about 89f tarmac temp 154f (and 214f where a truck had dropped some oil earlier) Even Intel chips are ok to 100C or more (had a Xeon running quite happy at 98 C)  Just went back through some posts, I said last October to have it checked at 220F but it's failing way before that. Did you tell ignition people you've been online looking for help?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 06, 2019, 22:30:25
There is something wrong with that ignition. 145f is pretty hot but if built properly it should still be working. If it's got a thermal overload cut out  it's set wrong I guess. There has to be a reason it's getting warm though, 120f isn't particularly hot for most motorcycle (or automotive) components inside engine bay area. I used non contact thermometer on the tarmac out side the house last week. Air temp about 89f tarmac temp 154f (and 214f where a truck had dropped some oil earlier) Even Intel chips are ok to 100C or more (had a Xeon running quite happy at 98 C)  Just went back through some posts, I said last October to have it checked at 220F but it's failing way before that. Did you tell ignition people you've been online looking for help?

I didnít tell him i had been looking for help online. I agree 140 isnít hot for that motorcycle. The jugs get well past 200. It will be interesting to see what he comes back with. Itís like I told him: I need this thing to be a beast on the interstate. A dependable beast. I put close to 30,000 miles on it already, and ultimately I want to run coast to coast on it. Iíll throw away all hopes of it looking good, if I can have dependability and power.

He claims I can have that. We just have to work out the issue. As long as he works with me Iíll  try to be patient, but if push comes to shove Iíll go another route.

I like having the simplicity of not having that Honda wire harness


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: clem on Jun 07, 2019, 10:21:35
I know that you don't have the ignition in your hands but something I've done with troubleshooting electronic overheating is to use freeze spray. I don't remember the exact name of the product though it should be common. I had an amp that would overheat and begin to fail. I went down the line and sprayed components with this until the amp would come to life again. Once I found the suspect component, I was able to sit there and keep freezing the chip every several seconds and the amp would stay on and function normally. A similar approach could have worked in your situation. I hope they get it sorted out for you.

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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 07, 2019, 23:40:21
Thatís a pretty good idea. I should hear something back next week. In the mean time, Iíll work on collecting a few odds and ends. I need to sort out the cockpit area. I would really like to shorten some cables and the front brake lines.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: CrabsAndCylinders on Jun 08, 2019, 01:19:12
I know that you don't have the ignition in your hands but something I've done with troubleshooting electronic overheating is to use freeze spray. I don't remember the exact name of the product though it should be common. I had an amp that would overheat and begin to fail. I went down the line and sprayed components with this until the amp would come to life again. Once I found the suspect component, I was able to sit there and keep freezing the chip every several seconds and the amp would stay on and function normally. A similar approach could have worked in your situation. I hope they get it sorted out for you.

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Would that product be CO2?  It exits an extinguisher at -66 deg C and does not harm electrical components.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: irk miller on Jun 08, 2019, 10:35:40
Would that product be CO2?  It exits an extinguisher at -66 deg C and does not harm electrical components.
Tetrafluoroethane.  Most brands label it as Freeze Spray.  Very similar to R12.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: cxman on Jun 09, 2019, 10:07:11
squidhunter i sent you a pm
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: CrabsAndCylinders on Jun 11, 2019, 03:01:05
Tetrafluoroethane.  Most brands label it as Freeze Spray.  Very similar to R12.

Cool!  I know that some electronic guys do use CO2 but the product you mention might be more suitable.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 12, 2019, 23:30:35
squidhunter i sent you a pm

Sorry, I just saw this. Sent you a reply. My job is nuts all week


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 12, 2019, 23:43:18
The good thing is, while the bike has been down Iíve had time to think about what I really want to do. I keep coming back back to the same conclusion: cosmetically, I want to change the tail and tank and after that all I care about is function. My problem with the tank is only that the stock one is worn out. It needs a lot of work. The tail is just unappealing to me. The good thing is, the bike actually rides really good.

Iím really needing to focus in on cleaning up the electrical. I feel like lowering the battery down would be better weight distribution, but Iím limited on how much fabrication I can do at the moment. Aside from that, Iíd like to introduce an m-unit. I like the idea anyway. It would be nice to have blinkers and a horn again.

Iím interested in you guys opinions, and experience etc. Iím trying to make the right decisions with this one. Not too many f models available here


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 21, 2019, 21:16:07
Talked with power arc yesterday. He still wasnít able to replicate the failure I was experiencing. It has to have something to do with the optical pick up. Heís replacing the optical pick up. Heís going to send me the old unit, and a new prototype.

After I get them, and test them Iíll post another update. I feel like itís something simple and I donít want to give up on it


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jun 21, 2019, 22:56:31
The "whale tail" on the F is kinda awkward. (as well as the tank) But, without it you have that HUGE azz tail light hanging out there with gnarly wires running around. The rat bike I did over the winter was missing the piece under the tail that filled it in (and had the HONDA lettering). They are real hard to find, so don't trash yours! I filled mine in by gluing together pieces of ABS from a wrecked GL1800 that the Honda service department saved for me. So, if you come up with an idea for what you'd like  to do with the area behind the seat (changing the seat will increase options), using busted-up ABS is an option for putting something together. ABS plumbing cement glues that stuff together real well.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 22, 2019, 00:25:19
The tail is pretty displeasing, but itís a bit iconic as well. Itís all there. The bike is very much complete, itís just really showing its age. Im fairly certain I can make a 77 tank fit. I would love to know if anyone has ever fit a 450 or 350 tank on one..... a 70s model. I would like to narrow the top a little more so the motor is more prominent. After all, the motor is what makes that bike special. The good thing (in my opinion) about the f model is the 19 front and 18 rear wheel instead of the 16.
Itís going to be tough to chop it up tho. Everything still functions well. I wish it were an easier decision


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jun 22, 2019, 07:49:09
To make the engine stand out more, just pull the valve cover off and polish the crap out of it, then polish the timing and alternator covers. But yeah, it is kind of hidden tucked under that big tank. A smaller tank is going to dictate a lot more frequent fuel stops, though.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jun 23, 2019, 17:01:01
Iíve thought about the frequent fuel stops. The truth is after 100-125 miles, I need to stop any way. The bike currently gets about 250 miles to a tank of gas


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 02, 2019, 21:16:39
I got my ignition back. Gary replaced the module. He said it looked like a pinched wire, which is totally possible. Iím not too crazy about the placement of the exit shaft which was milled by cycle x. But anyway..... Gary sent some new coils too, which Iím pretty excited about. Iíve almost got everything wired up. Should know something by the end of the week. Fingers crossed. I hope this is it


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 02, 2019, 21:19:36
Hereís the new coil set up. Two packs daisy chained. Theyíll wire straight to the battery, with a fuse of course


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: Sonreir on Jul 03, 2019, 11:35:58
How are you going to turn them off if you wire them straight to the battery?
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 03, 2019, 13:53:45
Safer to wire them through a 30A relay, that way you can turn them off when ignition is off. Easier than disconnecting every time
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Jul 03, 2019, 20:48:54
Maybe he wants to burn the thing to the ground.....  Or hopefully meant he was going to use a relay but went for short form explanation.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 04, 2019, 20:28:14
The ignition module controls the work coils. Same with the last set I had. No risk of burning the bike to the ground. Iíve already got it wire up. The coils switch on when you fire the starter. Iím not an electrical engineer, nor do I care to be one. Thatís why Iím on board for simple design. Also, if it does burn to the ground weíll have all learned a valuable lesson. Iíve ran fuses and such. Honestly I feel pretty confident this time around


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 04, 2019, 20:40:46
Safer to wire them through a 30A relay, that way you can turn them off when ignition is off. Easier than disconnecting every time

I did a relay bipass with the stock ignition, when it was on the bike. Honestly, if I would have ran better coils that would have been an awesome set up. These power arc coils are controlled by the ignition module. They arenít grounded. If I grounded them then there would definitely be a melt down


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 04, 2019, 20:43:37
All this being said, Iím not advocating for power arc yet. I havenít had any success with the system yet. They are communicating with me, however, and Iím installing it as instructed.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 05, 2019, 23:56:37
So, after working on the bike for hours the damn thing wonít crank. Iím getting spark, and the timing is right. I spent meticulous hours on the wiring....... and all I get is the occasional backfire. Iíve got a sneaking suspicion he sent me a module for SOHC. I just know it. Iíve checked everything and re-timed the damn thing several times.
Trying not to let disappointment set in


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 06, 2019, 00:24:49
If that even matters....


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 06, 2019, 01:24:44
Ok, so after another try or two Gary calls me. We decided it sounded like 180 out of time. All I did was switch 1 and 4 plug wires to 2 and 3. Then 2 and 3 to 1 and 4 and it fired right up.... damnedest thing Iíve ever seen. Test ride tomorrow!!

The coils put out one hell of a spark. It audibly sounds like a taser. If all goes well, a little tuning will make this bike sing. Iím trying to keep my feet on the ground tho. Still havenít ridden it yet


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 06, 2019, 07:27:19
Fingers crossed for ya.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 06, 2019, 22:09:24
Just got back from my shake down run...... bike runs amazing. I only rode about 50 miles, but I had zero issues. Idle was smooth. No backfire even on deceleration. No flat spots on acceleration. At the moment Iím very pleased. Iím going to take it on a good long run tomorrow and see what happens.

On a totally separate note: I cleaned my carbs really well last time I pulled them. They sat in a heated ultrasonic for 24 hours. I havenít had any carb related issues since, but they are always around the corner. Does any have any recommendations for a professional that does carb restoration? I think next go around Iíd like to spend the extra money and have them done really nice. I know some of the press ins could probably use some attention, and the slide bores are beginning to score a bit


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: Pete12 on Jul 07, 2019, 07:45:07
Great news, well done.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 07, 2019, 09:17:10
Mike Nixson, J.R. Luksik are two top rebuilders. To keep them running great, pure 100% gas (with good inline filters) and an occasional dose of Techron or Seafoam (aboht every 4th tankful) at label recommended rates can help keep things clean. But, don't use at higher concentrations than the label sez!
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 07, 2019, 21:05:50
Mike Nixson, J.R. Luksik are two top rebuilders. To keep them running great, pure 100% gas (with good inline filters) and an occasional dose of Techron or Seafoam (aboht every 4th tankful) at label recommended rates can help keep things clean. But, don't use at higher concentrations than the label sez!

Sea foam sounds like a good call. Non ethanol is pretty hard to come by out here. In Virginia it was all over. Iíve only found one place here.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 07, 2019, 21:10:19
Took the bike on a long ride today. I rode all the way to Georgia and back. I even rode through a wicked hard thunderstorm. No problems at all. I almost canít believe it.



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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 07, 2019, 21:33:04
Sea foam sounds like a good call. Non ethanol is pretty hard to come by out here. In Virginia it was all over. Iíve only found one place here.


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Techron is good maintenance too. Doesn't really matter if real gas is hard to find - carbs hate alcohol. Injectors can handle it. Try https://www.pure-gas.org/extensions/map.html (https://www.pure-gas.org/extensions/map.html)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: wozza on Jul 07, 2019, 21:42:52
Find a supplier for avgas :)....gone are the days of riding up to the local airport honking your horn 3times, then the fuel truck would come over to the fence line when he had a few moments free...
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 07, 2019, 21:57:47
Iíll have to try out the Techron. What brand do you use?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 08, 2019, 15:04:54
Techron is a Chevron brand. Fuel injector cleaner? I don't remember where I read article but I saw something couple of weeks ago about E10 fuel and stochiometric ratio's. E10 needs 14:1 instead of 14.7:1. Wish I could remember where I saw it to post link. It's a big con by farming' lobby to get worse gas mileage and pay more for it. The industrial giant's growing corn to turn into alchol have conned probably billions by now, small farms cannot compete
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 08, 2019, 17:38:43
Techron is its own brand. Here, we can get it at Advance Auto Parts or Walmart. Some top-tier gasolines have it included (Texaco is one).
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 08, 2019, 22:55:37
Techron is its own brand. Here, we can get it at Advance Auto Parts or Walmart. Some top-tier gasolines have it included (Texaco is one).

I just picked some up at advanced. Probably still gonna have to pull the carbs. Idle is starting to creep on me a little. This does not please me


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 09, 2019, 01:10:57
Could someone drop some polishing tips, or point me in the right direction?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 09, 2019, 01:31:28
For polishing.... aluminum? My drill press with belt changed for highest speed and abrasive loaded plastic fiber wheel (for really rough) followed by hand wet sanding with 240 >>>2000 grit followed by cotton buffing wheel on the drill press and jeweler's rouge. All available at Harbor Freight. Patience and elbow grease you supply yourself.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Jul 09, 2019, 02:25:12
10" sewn wheel running at 3,000 revs and use gray (emery) abrasive which they say is for stainless.  It should cut through the old laquer and scratches like you cannot believe.  Wear gloves and eye protection and hold on tight. Buffing wheels can throw parts across the room if the dig in.

After that go straight to a loose wheel with white rouge and bring up the color.  Only use wet and dry paper if there is a lot of metal to be removed - and it's still quicker usually to just buff.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 17, 2019, 12:23:14
10" stitched cotton wheels takes a hell of a big motor to turn.  I use 8" on a 1.5hp motor and can easily  stall it out. You don't need to sand to 2000 grit, I find  6~800 plenty when using dark grey or black compound. Use 'loose' cotton wheels and brown compo for primary  finishing and an 'open' soft cotton wheel to get mirror finish (also lasts a lot longer between polishing's). Solvol or Mothers is actually too rough for a real good shine after mirror polishing and will dull surface leaving scratches,  Use old well used cotton T-shirts, they are softer than re-cycled plastic
  If you going to use an electric drill, use 3"~5" surface speed on smaller ones is always too low for a good finish mops. 
  Sand any real rough stuff with 80 grit first then work up to finer stuff. If you can remove covers (or have spares) use a larger wheel. I often use stitched Sisal with emery compound if I'm not doing any sanding.   
 Basically you try a higher grit depending on original surface finish, cast or pitted need very rough to cut it down, 'factory' finishes you can generally start with 240 after removing any lacquer or paint.
   You can also make emery wheels if you get water based cutting compound, just soften the compound, add a little PVA glue then rotate wheels through 'mud' and allow to dry on the wheel. To reduce cut use ordinary red/brown compound.
  The alloy polishing set at HF isn't very good but can be made to work.
  Black emery compound from Home Depot is better than any of the other cheap sticks. If your going to do it properly you need to get stuff from Caswell but they are a little pricey sometimes.   Oh, BTW, it's great to hear you finally got bike running properly  8)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 18, 2019, 01:03:11
Caswell makes polishing compound? Interesting. I used their tank liner and it was the bees knees. Iíll never use anything else. It was 50 bucks, but it did the job right. I imagine their other products are up to par.
Yeah, the bike has been running phenomenal. I am starting to get some of the typical carb symptoms though. I know itís coming. I did run some Teflon through a tank. Seems to have made an improvement. I got a big bottle, so Iíll run about 4 oz every three tanks or so and see how it goes. Iím thinking I should check the sync for sure. Iím getting the dreaded clutch chatter


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 18, 2019, 23:06:36
So today, I get the bike out to tinker with the carbs, I go to start it up and I canít get it to fire. So Iím like ďscrew it, Iíll pull the carbsĒ. With the tank off I found my issue. Bank 3 and 4 choke butterflies werenít moving. The spring was attached it was just sticking. After I pulled the carbs and fixed that issue, I warmed the bike up good and resynced the carbs..... mmmm mm,  buddy she purrs like a kitten. Clutch chatter gone. Idle set perfect at 1100 rpm. And for the first time I did it in under an hour. I hate to say it, but these bike will teach you a carburetor lesson or two


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 21, 2019, 23:41:11
Since the bike has been running good, I decided to figure out the pannier situation. The last trip I took, I used some soft bags that threw over the seat. They actually held too much stuff. I didnít use half of it, and they made the bike heavy. They were also sliding up on me as I braked, and I couldnít use my grab bars to get the bike on the center stand. Pain in the ass packing and unpacking every day. So hereís my idea, and I just used stuff I already had. I cut two sides off a milk crate. I know how it sounds and looks, but as far as functionality goes itís perfect. I can strap all kinds of stuff to them. I mounted them on some bar mounts, and zip tied the bottom corner to the passenger peg for stability (temporarily, but it actually works well). I used to own a photography business, so Iíve got some nanuk 910 cases laying around. Rok strap that sucker on the panel and go. I like the idea of using things that are easy to come by, in case something happens on a trip I can easily find replacements. My plan is to pack one of my 910s with a film camera set up. The other one will probably be my jet boil and coffee set up or maybe tools, id like the weight to be even. Then Iíll use a roll top on the tail. Iím pretty close to figuring out a tail rack made out of tire spoons that you could use in a pinch, but Iím not quite there yet


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Jul 22, 2019, 08:52:12
Wish I'd known your need a couple months ago. I'd have given you my rat bike rack instead of selling it on the bike. Rear racks are sooo useful!(https://uploads.tapatalk-cdn.com/20190722/bd7c2b05361f2dd552558c887ab1cb51.jpg)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 22, 2019, 09:05:27
I had a rear rack for mine, and now I canít find the damn thing. The original panniers too. They were pretty rough though


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 22, 2019, 16:41:32
Wow, the original Honda rack and panniers were designed for the bike and look much better than most aftermarket. Even rough they would be a great addition. I've always preferred panniers to a rear rack, never liked having weight way up high and way far back. Really messes up the handling
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 22, 2019, 22:03:32
Wow, the original Honda rack and panniers were designed for the bike and look much better than most aftermarket. Even rough they would be a great addition. I've always preferred panniers to a rear rack, never liked having weight way up high and way far back. Really messes up the handling

Iíll have to find them. I had them in storage, then when we moved back everything is everywhere. I never could get the tail rack to match up right after I took it off. I must have misplaced some pieces. The panniers were already off the bike. They were really rough. I was sure they wouldnít keep water out, which is a deal breaker for me. My ultimate goal has always been to be able to carry some photo gear. Either way, I do need to locate them


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 25, 2019, 20:40:49
If I remember right, there were a bunch of thick wall spacers holding the brackets in place. The instructions for fitting were pretty comprehensive and easy  but I haven't seen them since about 1979. If you can find instructions it will give lengths of spacers from the fitting kit, I doubt the fitting kit will be available anywhere but at least you'll know whats missing
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 28, 2019, 20:29:03
Hereís a picture of my set up from today. I rolled my rain gear up in a blanket. Iím planning on using a dry bag about the same size. I really just wanted to test it out. Took this set up on a long ride today, on the curviest roads I could find. Held up surprisingly well. I canít say Iím 100 percent pleased, but everything functions properly. One case holds my camera gear. The other holds camping/cooking gear. The dry bag on top will hold sleeping and rain gear. Itís a ton less than I carried last time, so itís much lighter. Center stand still functions. I like it. Letís camp


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 30, 2019, 18:53:53
 8) even without pic.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: teazer on Jul 30, 2019, 20:01:12
There used to be a rack on the market that came with low or high sissy bars. 

Run it solo with a light back on the rack or fit the high sissy bar and slap you big bag on the passenger seat up against that tall sissy bar. For the life of me I can't remember what they were called but they worked well. 

With my old T100 I used a bag on the Manx style tank which allowed me to use it as a chest rest on long runs and kept the weight forwards.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Jul 31, 2019, 17:11:35
My 550 was faster with a tank bag, obviously helped the aerodynamics. Kinda weird that set up for touring with tank bag plus tent and sleeping bag tied on rear it would do around 130 with less effort than 'naked'
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2019, 21:44:31
8) even without pic.
Iím not sure whatís going on, but for some reason I canít upload photos 🤷🏻‍♂️


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Jul 31, 2019, 21:48:08
A high tank bag sounds like a good idea. When Iím on the road Iím constantly searching for new positions to set in especially around or after the 100 mile mark.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Aug 04, 2019, 18:02:21
I had a two piece tank bag, lower section straps to tank, about 5" high then top section zipped onto lowert for carrying more stuff. Pack it with whatever that's relatively soft and you can more or less lie on it, 200+ miles no problem
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 12, 2019, 22:04:26
Apparently I can load photos again. Hereís my camping set up from this weekend. I only camped one night, and this is all just the things I need. The good: I didnít over pack, and I carried my favorite film camera and several lenses. The bad: my tent sucks..... itís a cheap pole tent. Itís small and light and easy to put up, but itís a pain in the ass to get in and out of it. Also not too stoked on my sleeping pad.

I got a late start and my headlight blew while I was barreling down a dark highway. Thereís that. What was worse, the light bulb is apparently made of unobtainium. So hereís what I did right. I pulled over immediately first of all, calmly and slowly. I always pack my bicycle light. Itís actually very bright. I used to cycle a lot and that was my headlight. I zip ties that up, and used it as a temporary headlight to backtrack to a parts store. Like I said, swapping the light bulb would be too easy and of course the didnít have it. I bought a tool an automotive bung and a headlight (3 prong) for about 40 bucks total and wired that mother up. It took a total of about 10 minutes and I was back on the road. And now I can find lightbulbs anywhere lol. Everything else went well enough. I did feel like the bike smelled a little ďrichĒ, but it ran amazing. Is that possible? No backfires or anything. Cranks fine idle is great. I do think Iím getting a little noise from the front wheel bearings. Definitely going to inspect that further.

Ultimately need this bike to make some real trips. Not because itís convenient, but more or less for the challenge of it. Thereís something about making this bike dependable enough to actually ride is an obsession of mine.

Looks are totally secondary to me at this point


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: clem on Aug 12, 2019, 22:35:47
Nice side cases. I might have missed it but how are they mounted?

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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: Sonreir on Aug 12, 2019, 22:39:15
That sounds like a heck of a journey. I did a similar camping trip a few years back and lost an o-ring on my fuel line. I ended up holding the thing closed with my finger while a friend rode to the nearest town (15 miles each way) and came back with a selection of o-rings. Luckily one of the SAE ended up fitting and we were down the road again.

For lighting, I always set up an auxiliary option after having a similar experience as you. http://www.sparckmoto.com/Products/Detail/84 (hint, hint ;D)
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 12, 2019, 22:57:43
Nice side cases. I might have missed it but how are they mounted?

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I tried to post photos of it. Hereís a close up. I cut the sides off a milk crate and used some bar mounts to mount it to the side grab bars. Iíve been using the passenger pegs to stabilize them. So far theyíre working great


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 12, 2019, 23:05:52
That sounds like a heck of a journey. I did a similar camping trip a few years back and lost an o-ring on my fuel line. I ended up holding the thing closed with my finger while a friend rode to the nearest town (15 miles each way) and came back with a selection of o-rings. Luckily one of the SAE ended up fitting and we were down the road again.

For lighting, I always set up an auxiliary option after having a similar experience as you. http://www.sparckmoto.com/Products/Detail/84 (hint, hint ;D)

Well, the funny thing is Iíve set up such a light. I mounted a fog light to my crash bar. The bad thing is Iíve just been riding around with it like a ding dong. I havenít figured out the switch situation for it. Well, Iíve figured it out. I havenít executed it yet..... so thereís that. Lol

Iím glad it happened safely, and I gained a learning experience. Iíve definitely thought about it, just didnít think about not being able to find a bulb. Definitely thinking about going with an led headlight now, I like having my headlight switched on the light though. I wonít everything impossibly simple


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 12, 2019, 23:09:43
Well, the funny thing is Iíve set up such a light. I mounted a fog light to my crash bar. The bad thing is Iíve just been riding around with it like a ding dong. I havenít figured out the switch situation for it. Well, Iíve figured it out. I havenít executed it yet..... so thereís that. Lol

Iím glad it happened safely, and I gained a learning experience. Iíve definitely thought about it, just didnít think about not being able to find a bulb. Definitely thinking about going with an led headlight now, I like having my headlight switched on the light though. I wonít everything impossibly simple


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Those lights look the business man. So two can act as a headlight? I like that idea. Trying to get away from bulbs for sure. What kind of power draw do they have? Iíd like to talk more


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 12, 2019, 23:41:56
Iím thinking about making a tank bag. Something more proper. I just canít find what I want for sale....


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Aug 13, 2019, 08:58:56
I replaced the front wheel bearings on the rat bike '79 CB750F last winter - pretty easy. Drilled two holes in an aluminum bar to accept drill bits (backwards) that fit the keeper holes. Drilled out the stakes from the keepers (you don't have to go deep). The aluminum bar was long enough that it gave good leverage and spun the keeper out easily. Make sure caliper alignment is correct when you put it back together.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 13, 2019, 09:44:27
I replaced the front wheel bearings on the rat bike '79 CB750F last winter - pretty easy. Drilled two holes in an aluminum bar to accept drill bits (backwards) that fit the keeper holes. Drilled out the stakes from the keepers (you don't have to go deep). The aluminum bar was long enough that it gave good leverage and spun the keeper out easily. Make sure caliper alignment is correct when you put it back together.

Whatís the secret to the caliper alignment? That may be the noise Iím hearing. I kept thinking the tire was scrubbing the front fender, but I havenít been able to put my finger on it. Could it be the caliper rubbing?


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: pidjones on Aug 13, 2019, 12:41:52
Most Hondas that I've worked on have a bolt on one end of the axle and the other end is smooth. You tighten the bolt and axle holder (front first) on that fork and leave the other axle holder a little loose. Then you bounce the forks to let them center and tighten the other axle holder and check caliper-to-disk clearance on that side with a feeler gauge (provided in the onboard tool kit). Should be instructions in the FSM, maybe also the owner's manual. 0.7mm feeler on a GL1000, probably vlose to the same on yours. Check between disk and bottom and top of caliper. Loosen holder and re-center if necessary. The axle bolt side can't be adjusted.
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 13, 2019, 13:22:48
Most Hondas that I've worked on have a bolt on one end of the axle and the other end is smooth. You tighten the bolt and axle holder (front first) on that fork and leave the other axle holder a little loose. Then you bounce the forks to let them center and tighten the other axle holder and check caliper-to-disk clearance on that side with a feeler gauge (provided in the onboard tool kit). Should be instructions in the FSM, maybe also the owner's manual. 0.7mm feeler on a GL1000, probably vlose to the same on yours. Check between disk and bottom and top of caliper. Loosen holder and re-center if necessary. The axle bolt side can't be adjusted.

Iíll see if I can find it in the FSM. Thatís a good call.


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Title: Re: Dohc Cb750f: possibly a valve issue
Post by: crazypj on Aug 13, 2019, 16:54:25
If you have FSM, check axle is fitted into wheel properly. It's very easy to fit it from the wrong side and have the wheel off centre
Title: Re: Dohc Cb750f: possibly a valve issue
Post by: SquidHunter on Aug 14, 2019, 13:09:58
If you have FSM, check axle is fitted into wheel properly. It's very easy to fit it from the wrong side and have the wheel off centre

I do have the fsm, and the wheel and axle are mounted and torqued properly. It doesnít say anything in there about any alignment issues. However, I believe I found the noise. Iím thinking itís the speedo gear low on grease. Iím planning on deleting it anyway


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