Balancing act.

I've been tinkering with balancing the Fox .29 and .35 stunt engines. They have an iron piston and no counter weighted crank shaft to speak of. Lately most folks say to balance the prop. I say leave it alone and put it to use. The late Duke Fox published a sheet on hopping up the .36 engine. He recommended removing material from the crank shaft near the crank pin. That says to me the little counter weight is too small for the piston/ rod combo. So adding weight to the counterweight is the way to go. Well that is not easy to do. I figure that the props heavy blade in line with the counterweight will hep a bit. I also sawed a prop weight from 2 ounces to 1.1 ounces for plane balance and put it on the prop balancer and found the heavy spot. I put that on in line with the counter weight too. The engine ran much smoother. I will remove more weight from the prop weight and see if it runs smoother yet. Most modern engines, including the newer Foxes have a machined off area near the crank pin for balance purposes. They vibrate but dont have iron pistons to contend with. So they run smoother without any other mods. Still the heavy blade trick will make them run smoother too. I bench tested the engine and used a glass of water near the engine to show vibration. The fuel in the tank had a few ripples but nothing to affect the running of the engine.