ballastboy, the fins to take a lot of power from the engine. Its best to have them removed if your going to put a prop on the engine. The boss's near the center of the flywheel are what the pullstarter need to operate. If your having trouble getting someone to turn down the flywheel on a lathe for you( this is the best method, not grinding) Peter Faith at www.wackerengines.com sells the flywheel ready to fly for $15 and the best carb to make some real horsepower for $17 I believe, he even has the prop hubs and engine mounts for these engines. Piper

BTW, you want to rebalance the flywheel after you remove the fins, Peters are already if you buy one from him.