The Superstar flies very nicely if you line up the engine dead straight, without any right thrust, or especially, not any left thrust. If you can't get it straight, a very small amount of right thrust is acceptable (this means that the engine points very slightly at the right side of the nose when looking at it from the tail end of the plane).

A simple but effective way to check the alignment is to sight along the cooling fins on the cyl head, looking from the front of the plane -- it is easy to see if the engine is cocked one way or the other.