A sticking centrifugal advance can cause those symptoms.
GlockPointer wrote:
Barney rules! Took the red 90 to the beer store again today. It wants to idle high today as apposed to the yellow 90 which has yet too idle for me. Also the idle hangs up if you blip the throttle. Then if I turn down the idle it's suddenly not enough. If I just ride there are no problems. I'm too lazy to swap carbs around tonight.



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Q (Quantum Mechanic)

1968 CT90/140
2007 Lifan 200
2005 Zongshen 200
1981 Honda GL500 Interstate