Engine Run Away

[donb4103]

I have never had this problem until today. A customer brought their bike to me to fix it. Well when you get it started it performs just right as long as you are riding with the engine pulling you. But as soon as you pull the clutch in the engine just takes off and will not idle. I have checked the cable 3 times and even replaced the carb with a new one and everything slides and works perfectly. The cable has no binding and seats perfectly every time. Could it be sucking air from somewhere and causing it to not want to idle? If I let it run like that for a few seconds it will finally start to idle down but it takes several seconds and the cable is all the way into the carb while it is running so fast.

 

[crassius]

I'd spray some water around the intake to see if there's a leak.

note: I've had some engines that were well tuned that ran a way high idle until they warmed up for a minute or two - I assume it is acting lean because the cold engine wants to be richer until warm

 

[2door]

You didn't tell us what engine you have but we're assuming it is a Chinese 2 stroke?

What you describe is typical of an air (vacuum) leak somewhere downstream of the carburetor. Have you looked at the intake manifold gasket? Are you sealing the carb to the manifold or using an 'O' ring?

Crankshaft seals could also be the problem. There are two, one on each side. One is behind the magneto rotor and the other behind the small, primary gear.

Case half gaskets can also be responsible although that is rare compared to the other two areas I suggested.

Tom