ORIGINAL: Rcpilot
Grind a little off the backside of the cylinder transfer ports to smooth fuel flow. It's very common for the car guys to mod their engines in this fashion. The car guys also notch the crankshaft counterweight some how. I think they call if "knifing" I am not sure exactly what it does, but I think it is supposed to allow smoother flow of fuel from the crankshaft into the crankcase.
I myself am a "car guy" and its not called "knifing" actually I've never heard that before, I've modded some engines before, and it sounds like plane engines tend to peel (the lining peel) but cars theres not to many that do that, and car engines are turning 40,000rpms, but what you are talking about when you cut the counter weight, there called "turbo cuts" the help mix fuel and air, and flow, but to much can cause the engine (or the crank really) to vibrate and blow your bearings inside there. but plane engines don't turn to the rpms the cars do, so vibration will not be as bad.
but from what I know modding a car engine is different then modding a plane engine. I know downunder knows some stuff about modding plane engines.