clutch? maybe

[VenturiEffect]

Well the bike starts up fine. Has tons of power and good throttle response. But once it gets has been 2 miles it starts to act funny. When I pull the clutch in and let go of the throttle it goes erratic and take a bit to wind down to idle. By erratic I mean it goes brap brap pow brap brap brap pow brap pow brap brap pow and then purs. I know the is no air leaks. Im sorry if im having a hard time explaining this.

 

[2door]

You didn't say what engine you have but we're assuming it is a Chinese 2 stroke.

In spite of what you say, "no air leaks" your symptoms are consistant with excess air entering the engine downstream of the carburetor. If you're certain that the carb is sealed to the intake manifold and the manifold to the cylinder then my guess is you have a bad crankshaft seal. The one behind the magneto rotor or the small, primary gear might be the culprit. If you change them, change both to be sure.

Tom

 

[crassius]

if the revs don't go high, it may be an air leak at exhaust (back in the day I'd drill small holes in exhaust to spit flames out the back when I slammed the throttle on my 750) - not engine going funny, just noise that sounds like it is