One thing I could say is make sure you have adequate exhaust valve clearence. Make it on the high side of the tolerance window[.008 or .009] rather down near .004. I have one of these engines and it gave me so much trouble at one time that I was ready to throw it away. until a friend suggested I set the exhaust valve clearance open more. That made a new engine out of it. It now flies flawlessly. I fly it every day. Some of those engines were quite sensitive to valve tolerance.