Its good to know it runs OK with that prop,at first I thought the lower pitch caused the problem but after going back to the 20X8 a second time it started acting up. With the 20X6 I got the mid-range I wanted-mostly 2-stroking and clean transition,I did tach the high end @ 8400RPM (20X6)but didnt leave it there for more than a second or 2. It must be something in the carb thats wrong?