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Discussion Starter · #1 ·
Hello folks,

I've been building a motorcycle for the last eight years and finally was able to get it started, which has opened a whole new level on problems to resolve.

I searched through various forums and articles but it seems I haven't found the reason for the problem, which consists of the following - the bike starts well but after a brief period of time, either parked or driving, say 5 to 10 minutes, the engine stalls and won't start again. The starter won't spin, i.e. engine doesn't crank, there is no click from the solenoid (but starter will spin if I short circuit it with a screwdriver), kickstarter won't work nor it would bumpstart. I found the only solution is to let it rest until it cools down.

I've tried and replaced battery, multiple starter solenoids, spark plugs, push button, ignition coils, but I'm very reluctant to give it a complete rewire as I suspect problem might lie with engine's increased temperature leading to more resistance to the wires. I've wrapped the exhaust with thermal tape but that didn't change a thing. Cooler days give it a few more minutes until the issue happens.

My hope is that someone might has had such a problem and they would share their thoughts on how to resolve it because honestly I'm very frustrated.

Cheers!
 

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You can download a service manual for the XS750 from https://www.carlsalter.com/mcpdf/Yamaha_XS750-2D.pdf
that's the closest to your bike I could find.
Based on the problem you described the first things I would check is the condenser (x3) in the ignition and adjust the valve clearances. A compression test might reveal an issue if the valves are out of adjust badly enough.
 

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If the valve clearances have never been visited on this bike it is likely a problem ... as your engine heats the very small valve clearance is further reduced to near zero, if the clearance is too great, once it reaches full operating temperatures you lose compression past the valve seats and the engine quits.
 

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Discussion Starter · #4 ·
You can download a service manual for the XS750 from https://www.carlsalter.com/mcpdf/Yamaha_XS750-2D.pdf
that's the closest to your bike I could find.
Based on the problem you described the first things I would check is the condenser (x3) in the ignition and adjust the valve clearances. A compression test might reveal an issue if the valves are out of adjust badly enough.
Hello, mate, thanks for replying! I' forgot to mention it's a TCI ignition so no points. Valve pads has been replaced recently according to manual and appropriate clearances. I will check again, thank you!
 

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Valve clearance issue would definitely produce the symptom you described, I've experienced that problem first hand and on more then one engine.

Is your engine running the original crankcase ventilation system? If there is a problem in that respect your crankcase pressure will elevate until that becomes a problem for the running engine, when it quits under those circumstances you should likely hear strange venting noises coming from the engine after it stalls.
 

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Re: this part:
"The starter won't spin, i.e. engine doesn't crank, there is no click from the solenoid (but starter will spin if I short circuit it with a screwdriver), kickstarter won't work nor it would bumpstart. I found the only solution is to let it rest until it cools down."
I'm trying to find something in the electrics that would account for this, what all have you changed from stock electrics? things like regulator change or adding accessories included
 

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Discussion Starter · #7 ·
Re: this part:
"The starter won't spin, i.e. engine doesn't crank, there is no click from the solenoid (but starter will spin if I short circuit it with a screwdriver), kickstarter won't work nor it would bumpstart. I found the only solution is to let it rest until it cools down."
I'm trying to find something in the electrics that would account for this, what all have you changed from stock electrics? things like regulator change or adding accessories included
Hey mate, I couldn't express my gratefulness for taking the time and looking into this stuff. Here's what my wiring looks like:

Wiring

I am almost sure there is a compression issue as well, however that wouldn't stop it from cranking, right? I've started to think some issue with the starter motor (brushes or whatnot) because this is the only thing that hasn't been rebuilt. Also the R/R is brand new.

Thanks again!
Cheers!
 

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Resigned back onto this forum for this post.

You might want to check your stator and flywheel... seems like if you switch and swap some years of these bikes the two aren't always compatible. They can spin freely cold, but bind when hot. Have you played mix and match with stator covers?

Put a temp gauge on that side case after it stalls and see if it's super hot. I recall I couldn't put my hand on it...

I swapped stator and cover then everything worked.
 
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