I have a 15 year old BME 44 (Echo) I've had since new. It runs fine but loses 800 - 1000 rpm from peak after running awhile. It has been in a WM Zero 14 years and never had cooling issues. The compression is really good and using Amsoil Sabre at 75:1. I rebuilt the carb a couple of times but no change. Even checked timing and tried another ignition. The engine bearings seem ok. It will run a full flight and has never quit so It is not overheating or getting too hot. It has gotten worse over the last few years I have never pulled the piston out of the bore since compression does not seem to be a concern It really looks clean thru the exhaust and carb port and on top of the piston and rings. Will buildup of carbon in the combustion chamber cause this problem? I'm stumped. Thanks, Paul