I have a YS63 that does not seem to want to idle below 4000 RPM after about 40 minutes of total run time. I have tried adjusting the idle mixture settings (started at 1.5 turns), but the engine seems to idle the slowest (4000 RPM) with the low speed needle all of the way in. Also, the engine will not shut down even with the butterfly completely blocking the carb.

As it seems that there is an air leak somewhere in the intake, I am considering swapping the gasket between the carburetor body and the back plate. Are the o-rings in the needle valves or the intake pipe likely causes for this type of problem. They seem to be in good shape from what I can tell.

Any help resolving this would be appreciated.

Thanks,

Bryce