I did break in the engine about 3 yrs ago on a sig 4*60. It ran good but has always sagged when pulling up hard. Never had the dead stick problems though. I am using an APC 12x6 prop. I tached it the best I could and it was about 11800 to 12000. I think I will put the stock muffler back on and leave the cowl off and try to get it running better. Then maybe i'll put the pitts back on and try plugging a hole.