well, the truth is out. It wasn't the heli engine, it wasn't the fuel tank or lines and it wasn't the 135degree mounting. The problem was caused by the heli muffler. I changed the muffler back to the tt46 muffler and all is well again. BUT, I LOST a LOT of POWER. I think I lose at least 1000rpm and the engine is actually warmer with the airplane muffler. Any idea why a heli muffler cannot work in plane?