Hi,

I have a YS 63 (not 63 S) that always runs great in first flight (cold). But from the 2nd flight on, it likes to lean out during the flight, normally after about 1 minute after taking off (power drop to 70-80%). Making it rich does not help. The exhause trace is relatively heavy (either in the 1st or subsequent flight). The engine has been "ported" by YS performance, and the fuel is 20/20.

Question: is the rear bearing going bad? What else can cause this?

Thanks in advance

--nsrc