my funstar with a tt50 heli engine and a heli muffler runs well upright and inverted, but not when the nose is pointing up. It slows down quick and quit. What could be the problem here? It idles very well too. The engine was previously in a seagull low wing trainer, it ran well, upright, verticle or inverted. Could it be because of the muffler? I was running it on the tt46 muffler previously in the seagull lw.