RE: O.S.Engine Question
I believe the SF was the forerunner to the FX. I have a .61SF helicopter engine that must be 20 years old and it still runs like a champ with plenty of power. I would put 3&1 oil in it and let it sit for a few years between projects, mount it on another boat, and it would fire up first or second try with an electric starter. I have flipped an airboat on the ground and had it land on its side and the engine would sit there running at a perfect idle. I do not know the differences, but both are great engines. Dennis