Also to clarify my compression post, what I meant is a loss of compression when the engine heats up. This happens to nitro engines when they're on the way to the nitro junkyard in the sky. What happens is as the engine heats up, the sleave expands and compression is lost. The engine will typically start up fine and run fine for a minute or two until the sleave starts expanding. The expansion happens in any engine, but an engine that is worn will not tolerate it. The engine will begin to bog down under higher rpm. At low rpm it will seem to run fine, but as you increase the rpm and accelerate the engine will sound like it just ran out of fuel. This is what's called "falling flat on it's face". When the engine is cold it will have a decent amount of compression when turning the flywheel by hand, but compare it to a good engine and you can tell the bad engine has moderately less push through the stroke.