Richard, mine runs great now. Lots of break in time, 2 head shims, small venturi , os .15 r/c needle valve. Gets very consistent runs with a slight break. My good runs came after changing tanks to a clunk with the uniflow running way to the back , just ahead of the pickup. After a lengthy break in time , it went from 6 minutes on 6 oz. to 6 1/2 minutes on 4 1/2 oz. Mounted on a P-40, it works great. I like it a lot , may buy another! Oh yeah, TT 11x4.5 prop and 10/22 fuel.