If the engine is mounted with the head on the right side of the airplane, it could be out of lateral balance. You can correct this with stick on weights under the left wing tip. If the wing(s) is warped, try having someone twist the wing and apply heat to the covering. That should take out the warp. Might take a few tries to get it perfect, but it can be done. You can visually sight along the trailing edge of the wing (looking from the tail forward) from several feet away to see the warp. Use a bright overhead light and the warp will be easy to see in the reflected surface of the wing trailing edge.

Paul