This could also be because of slight miss trimmed ailerons and rudder. Try retrimming the rudder in the direction to correct the corkscrew then readjust the aileron trim to get level flight in straight out flight. It is easy to get these two trims adjusted to give level flight yet be out enough to give you the problems you are having. It could also be because there is a slight wing warp and the trims needed to correct for that cause the corkscrewing loops. Just hope it is not the later as that is much harder to correct.