Your trim has to be set to zero or your opti drive will think you have the throttle on and not let you shift. My experience has taught me that there is not need to ever adjust the throttle trim unless your servo is way out of whack. All of the idle and tuning issues should be done on the carb and not with the throttle trim. If you use the throttle trim to adjust the idle you are effectively eliminating the throttle stop screw. I hope this helps.