I am trying to fix my dads quad which is a 1994 (I could be wrong about the year) 350 trail boss. The problem it is having is that will not idle at all. At part throttle it will start without much issue, and it seems to rev fine, but as soon as you let off the throttle it dies. You have to feather the throttle to keep it running. Even if you keep it running, after a few minutes it will backfire and die. Last year my dad cleaned the carb multiple times. After tinkering with it for a while he had a work related injury, and has not worked on it since. I have also cleaned the carb, checked compression, and checked spark. All three look fine. I’m confident it is not the carb, or any fuel problem. I can’t find any vacuum leaks, the crank seals seem fine, and it had good compression. So, I’m thinking it is an electrical problem.

I should mention what happened when it went bad. My dad was plowing snow in the driveway when all of a sudden it backfired and died. He got it started and it was very sluggish, and wouldn’t idle.

The two things I am thinking are flywheel key and the throttle safety switch. I have not popped the cover off to check the flywheel key yet, but it was put on with RTV as a gasket last time. Is there some kind of fluid in there? As for the TSS, I honesty cannot figure out how it works. There are tons of threads online on adjusting it, but I don’t see how it does anything. It adjusts just like a clutch, you just loosen the lock and turn nut. They all say to set it about 1/8" off the contacts. The problem is no matter how you adjust it, the throttle always rests on the contacts. The throttle cable is one part, and the thumb throttle is another. I would like to eliminate it, but I don’t know if I should cut a wire to open the circuit, or connect the two to close it. Any other ideas are appreciated.