Every tank has a week in between I fly every sun.I tried to stick a piece of paper towel to get off but no use, I dont know the name of the part but its the big round thing, first thing you see when you take the backplate off, looks like a counterweight, that was the only thing with this rust looking stuff on it, I'm using wildcat 15%, I run a lil rich since the engine can run off of fuel iwith castor oil but I have to run a lil richer than normal