i went from 6 to 7 pounds 1/4 1/2 3/4 didnt seem to change much i dont have a video camara i tried leaving at 4200 early in the season but seemed the 60' was better at 3800. i dont think its bottoming out. it had about a 100 150 more hp than my motor plus it was aluminium headed and mine is steel headed so more hp and a little less wieght. i think im going to do what zip said and raise the top bars a hole and see what it does