For what it's worth, the "general rule" with 2-cycle engines in control line stunt competition is that the engine is almost always inverted. There is no loss of power. Starting is not a problem. A 2-cycle engine doesn't "know" if it is upright, inverted, profile-mounted, or at an angle. They are mounted in all these configurations on RC and C/L planes. Look elsewhere for any loss of power. (Old fuel, old plug, tank location, cooling provisions.) Good luck, Dzl