Hi Capin, Glad to hear from you about the 41 engine. I tacked my engine today and it turned a zinger 18x10 about 7020 rpm. I tryed a zinger 20x8 and turned it 6630 but with 1 lb. more pull on a fish scale. Still have not changed the muffler.Hope to get a few more rpms with that.The carb. is spitting a little bit of fuel out the velosity stack, anyone have an idear what would cause that. Thanks Wayne