I have a 1985 ATC in excellent condition. Tranny's good, engine's good, body great shape, etc. Anyway, quite some time ago, I was riding it, and it just shut off, like I just turned the key off. I tried to start it various times, but no luck. I also replaced the coil and spark plug during this time, both brand new.

I took it to a mechanic some time later (a couple years, actually, which was earlier this summer). He totally cleaned the carb, gas tank, etc, replaced spark plug, and said it started right up. Well, I got it home, run it awhile, and it did the same thing. Run for a little while, then just shut off. We have run it off & on all summer & fall, and it continues to do so. Sometimes it will run 5 minutes, then shut off, sometimes a couple hours. Sometimes when it shuts off, it will start back up in a few minutes, sometimes it won't. The other evening I also noticed that when I press the throttle, the head light dims (quite a bit, actually). When you let off and the engine rpms slow down, it brightens right up again.

I'm not very excited about hauling it all the way back to this mechanic, because I don't feel like he really knows what he's doing. When I called him and explained the symptoms, he told me that he wouldnt be able to tell what was wrong with it unless it also shut off for him, and said he hasn't got time to run it for 2 hours to see if it re-creates the problem or not. I understand, but that doesn't fix my problem.

Sometimes when it shuts off, it sounds exactly like it does if you switch the key off. Sometimes it will die a little more slowly, and once it starts dieing, you can't give it gas or it will kill it. In those cases, it idles for a little bit, then shuts off.

Any ideas or experience?

Any ideas

 

Ohm out the stator next time it dies. The older hondas have been known to have issues with the stators on older quads. All those years of heat cycles, makes the tiny wires brittle. One gets a crack, and when it warms up, the gap expands, and the continuity is broken.

 

It sounds like the engine kill wire is grounding somewhere
Had a buddy just spent about a week searching on a 79-ATC-90
Brittle wire insulation broke and would ground at worst times
Sometimes run minutes sometimes hour
Good luck
Ray

 

What model is it? I agree with a stator issue. When it dies and wont start is there spark? Fuel?