1977 Yamaha XS750 Electrical Problems

| 11/30/2011 5:03:00 PM

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1977 Yamaha XS750 Electrical Problems 

Q: I own a 1977 Yamaha XS750 with about 25,000 miles on it. For the past two years the bike has gotten more and more stubborn about starting, and the idle is getting rougher, too. The starter turns the engine just fine, but it won’t start the bike. However, when I kick it, it starts right away. Until it is fully warm, it will idle at 500rpm, stuttering and stalling unless I keep the rpm’s up with the throttle. Once warm, it will idle at 1,100rpm, but if left alone for a couple of minutes it will slowly stumble and stall. In your July/August column, I read about an issue with the reserve lighting on a XS750, and it gave me an idea to try turning off the lights before starting my bike. Sure enough, with the lights off, the starter starts the bike, and it idles much better (cold and warm).

It still is not perfect. Kick starting the bike usually takes four to six kicks when cold, and one kick when warm (lights on or off). Even with the lights off, the starter takes a couple dozen rotations, with me feathering the throttle to coax it to start. It also takes forever to warm up, even on an 80 degree day. Lastly, with the lights off it does idle better when warm, but it will still slowly stumble and stall. It just takes longer for that process to run its course. It seems like whatever the issue is, the lights exacerbate it. The bike runs great on the road, and the battery seems to be getting charged. Whenever I stop at a light or stop sign I am always anxious about the bike stalling. Here is what I did over the past winter to try to improve this starting and idling issue:

1. Installed an original exhaust system, replacing an old aftermarket system
2. Rebuilt the carbs, installed factory-spec jets
3. Installed new points and condensers, plugs, wires and coils
4. Timed the ignition
5. Synchronized the carbs
6. Checked the compression
7. Cleaned the air filter
8. Replaced the battery
9. Replaced the starter button. Cleaned all the ground connections in the switch housing (the starter button grounds to the handlebars)
10. Cleaned the main ground to the frame

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