Hello all , great board. First post, but I've been lurking for a while. I have a 98 175 exec Ocean Runner on a 20' Boston Whaler. It is most noticeable say at about 3500rpm heavy load, give it full throttle and you can feel it shake before it picks up rpm. I've pulled the plugs and they are all a medium brown. It is propped for holeshot and heavy load,SST 17 ,5600rpm.This is my second season with this set up and this problem, At the begining of the season a local, long time Omc master tech shop had it and changed a coil , flywheel, decarboned, and rebuilt carbs, no change. He now wants to pull powerhead and look for holes in block allowing cooling water to ruin tunning. Marty D