250 cu in IL6 w/ 2bbl carb, MC outdrive. last season, motor running ok. over winter, pulled outdrive and replaced bellows and gimbal bearing. this year, replaced plugs and adjusted points and timing. motor would not get over 3500 rpm in or out of water on muffs(runs @4500 WOT). plugs looked sooty. have replaced points and condersor, plug wires, fuel filter, rebuilt carb, rechecked timing (#1 and #6 cylinders), fuel volume good. outdrive sounds quiet and runs smooth. motor will accelerate up to ~3000/3500 rpm and stop increasing in speed. no smoke, no popping, but doesn't sound right. spark from coil secondary strong during cranking, ~10V at coil. is this anything outdrive R/R could cause? parts replacement getting expensive. 
