Engine help

superdave

Superdave
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So I just purchased a 1981 Yamaha xs650 custom bobber. Everything was great until I was going down the road and the engine power kind-of hiccupped? It was as if I abruptly rolled off the throttle except I didn't role off the throttle. It was then followed by a complete loss of engine power and the bike died. I pulled over tried to start it and it started right back up.
It did this several more times. Each time it got progressively more frequent. First time I went 3 miles then it died, next time 2 miles and so on. I spoke with the former owner and he pointed to the carbs, however after speaking with some mechanic friends and engineers they said if it was a carb issue I would have most likely lost power in one cylinder, but not both. Another friend thought he smelled something burning, like something electrical as opposed to gas. The gas is running smooth and clear no flow issues.
It's a custom bobber so we're going to pull the tank, double check the gas and wiring, but just wanted to throw this out and see if it rang any bells.
Thanks
 
Start with your battery. Should test at 12v off, running at 1,300+ rpm 14.5v. Work back from there. In the "tech" section on here there are some must reads in the "maintenance and general troubleshooting".
Did the PO (previous owner) have this problem before?
 
I don't know what fuse panel you have, but if its still the original fuse panel (4 position with clips holding glass fuses), that may be your problem. Their resistance increases and they can heat up.

Check all electrical connections that feed power to the igniton coil. Sounds like an intermittant electrical fault.
 
Hey thanks everybody, I'll take the info to my guys when we go to work on it Monday. I'll let you know. We're thinking sparkplugs? Or potentially a short in the wiring?...

Yeah the PO new about it. He down played it as only happening occasionally and attributed it to the carbs, but like I said my guys don't think the symptoms fit that diagnosis.

I'm located in Tucson Az
 
A frazzled TCI does exactly what you described. If you has the skillz check the solder joints for rings and cracks. I'm betting you'd find a couple and that fixing them would fix the problem.
 
Dave,

Welcome to the site! Since this thread is also your intro:

ttiwwop.gif
 
Transitor Controled Ignition..Where in Tucson? I'm just north of D-M AFB
 
Thanks for the welcome. I'll get some pics up as soon as i get the bike up and running and back from my buddies.
 
The TCI is the electronic ignition used on the 80 and up XS650's. Yours being an 81 had the TCI as stock. Do you know what ignition the bike has?
 
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