I have a 200cc - '89 (I think) Moto 4 shaft drive w/ reverse. It makes noise as after it revs up and gets moving, but it stops making noise as soon as you leave up on the throttle. It sounds like its coming from the bottom of the tranny/clutch area.
I blocked the rear end up and ran it through the gears and no noise. Could this be an issue with the syntrifical clutch or shaft drive?
Yamaha Moto 4 Noise
