I am getting ready to go to the track but what I think OS means when they say not through the carburetor is in the fuel nipple and the venture is OK. I have been doing all my OS and none OS engines like that for 6 years with out a problem. Fuel is VERY hygroscopic and I all ways use after run oil as it is just cheap insurance! I ran my buggy yesterday and I am taking it to the track today but I put after run oil in it. How much does after run oil coast and how much does an engine cost? If people do not want to run it that is fine but I all ways will. Even 1 to 1 alcohol racers purge their engine at the end of each day. I know when I ran my alcohol go-kart I did and every one I know did.