This is the second time my new .40 Tower Hobbies ABC engine sized. I have been able to free it up both times but I have yet to fly my plane because of this. I am using Omega 15% W/Castor pink fuel. The first time I thought it was because I was running the engine too lean but this time I'm sure the fuel/air was set right. Now I suspect it is happening because of an improper spinner size. Could it be happening because the spinner is too big for the engine crankshaft prop. backing plate and it is going out of balance? I know....I'm probably way off base here but I can't understand why this is happening. Any advice would be greatley appreciated.