We run 4*40 races and the only engine allowed is a ST 40 with a stock muffler and 10x6 MAS prop and all run 15% Cool Power. You should get between 14,000 and 15,000 rpm. If engine is new run 2 tanks (6 oz/tank) sloopy rich then let her rip. Keep fuel tank outlet on same level as carb inlet for best performance.