I had a similar problem with a Tiger Moth (of all things... they normally have no probelms) turned out to be a VERY minor warp in a wing. Check the incidences in several places along the span of both wings with a meter.

Mine was a hard right turn... full left rudder and full left aileron needed to level it with as minor a warp as I had... was unbelievable... (1/2 deg at the outer 1/4 of the left lower panel) Straightened the wing... trims were centered.