Thanks Ty and Bob , I use 10% 11/11 type fuel , I have added one head shim( I need to check I think .005") all kinds of props the one that comes the closest is Pro Zinger 11-4 sanded on edges. The engine seems to do ok with very different props it is just very inconsistant Throughout the run, even tried different style tanks. Right now it is running on a sulivan klunk with uniflow. Had this engine several years. even ckecked the alignment of the sleeve (did that when I got it) I will keep trying. I have another one I just bought from the LHS last week I think I will run it in on the bench and install it to see what if. Plane is a vector ARF.