Dohc Cb750f: possibly a valve issue

crazypj

Split personality, I fake being smart
SquidHunter said:
I
I’m still suspicious the battery I’ve 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 didn’t 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?
 

SquidHunter

Active Member
To be clear, I don’t have a charging problem. The cycle x charging system solves that. I’ve got an ignition problem


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crazypj

Split personality, I fake being smart
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.
 

teazer

Well-Known Member
DTT BOTM WINNER
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?
 

SquidHunter

Active Member
teazer said:
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. I’ve got too much going on this weekend, but over the next couple of weeks I’ll be digging in. There’s 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. Didn’t break down, because the cover was off, but it was erratic behavior for sure. It even seems like it’s running rich now. Doesn’t make any sense. Still running the airbox and stock jet sizes. I know it’s the ignition.


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SquidHunter

Active Member
crazypj said:
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, that’s what I thought too. I’m just fishing for opinions. I haven’t had any problems with the agm battery. I’ve been running it for 6 months without any battery/charging issues. I’m definitely having ignition issues.

I


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crazypj

Split personality, I fake being smart
teazer said:
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
 

SquidHunter

Active Member
crazypj said:
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 you’ve really got me thinking. The one thing that I’ve assumed is my wiring was good, due to the fact that it’s so simple. I’ve got to rewire it anyway, so I might as well pull it all apart and have a look-see.

What is everyone’s recommendations on wiring a bike? I’ve got good tools for crimping and stripping, so I haven’t been soldering my connections. Some say that’s fine, but my chopper friends say solder everything. After this experience, I’m 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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pidjones

Well-Known Member
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.
 

crazypj

Split personality, I fake being smart
SquidHunter said:
Now you’ve really got me thinking. The one thing that I’ve assumed is my wiring was good, due to the fact that it’s so simple. I’ve got to rewire it anyway, so I might as well pull it all apart and have a look-see.

What is everyone’s recommendations on wiring a bike? I’ve got good tools for crimping and stripping, so I haven’t been soldering my connections. Some say that’s fine, but my chopper friends say solder everything. After this experience, I’m 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
 

SquidHunter

Active Member
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 I’m going to attempt to complete the rewire. I’m going to change a few things. 1. I’m going to wire the coils straight to the battery 2. I’m going to wire the regulator/rectifier straight to the battery 3. I’m going to use the least amount of connectors possible


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crazypj

Split personality, I fake being smart
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)
 

SquidHunter

Active Member
I’ve got a fused relay that I was running on my stock coils, to bypass the ignition switch. According to power arc this isn’t necessary with their system. The control module turns them on and off ‍♂. That’s what they say anyway.

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


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crazypj

Split personality, I fake being smart
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 )
 

SquidHunter

Active Member
crazypj said:
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. I’ve got a 4 yo son. It’s pretty fun, but grandkids seem more fun


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crazypj

Split personality, I fake being smart
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)
 

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