I figure this is not the problem, but I did find it on mine. I put the pull pull on my US Lite and on the counter balanced part of the rudder, there as a little bit of the covering dragging on the fin part. When the rudder returned to center, it was a little off center. I took a covering iron and re-ironed the covering on the underside of the rudder and the top of the fin. This cured the problem.