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Author Topic: Dohc Cb750f: possibly a valve issue  (Read 3700 times)

Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #30 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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Offline themotoworks

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Re: Dohc Cb750f: possibly a valve issue
« Reply #31 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

Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #32 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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Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #33 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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Offline VintageMBike

  • Posts: 56
Re: Dohc Cb750f: possibly a valve issue
« Reply #34 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.

Offline irk miller

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Re: Dohc Cb750f: possibly a valve issue
« Reply #35 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. 

Offline teazer

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Re: Dohc Cb750f: possibly a valve issue
« Reply #36 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.

Offline kopcicle

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Re: Dohc Cb750f: possibly a valve issue
« Reply #37 on: Sep 01, 2018, 01:54:45 »
fsck'n Honda iggy bits
"If a man wants to carry two cats home by their tails, by all means let him. Heíll learn things that he might not have otherwise even guessed, and the experience will be one heíll not soon forget!"
~S. Clemens

If it leaks after all this? I'm gonna pull a "Brad" and bulldoze the fucker!

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As an equal opportunity bigot, I'll insult any brand, any style, any time...:wink:
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Offline crazypj

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Re: Dohc Cb750f: possibly a valve issue
« Reply #38 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
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline irk miller

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Re: Dohc Cb750f: possibly a valve issue
« Reply #39 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.