I deliberately under-proped it on the advice from Ultra -RC and seeing what other gasoline flyers(3-D) are doing in my area. This is done mainly for 3-D flying,I wouldnt run at full anyway since its way more power than the airframe needs. What I was trying to accomplish is getting the mid-range leaner so I have the throttle resolution needed to harrier & hover and allow the plane to fall in a hover. The engine ran fairly well with a 20X8 and Mej. 20X10,peaked at 7700RPM with those props but the mid-range is slobbering fat,nothing but 4-stroking. I did lean out the low end untill it surged,then richened a little with not much change in mid.