I just bought a 1985 150 merc blackmax. The motor runs a little rough at different rpms and speeds up and slows down without touching the throttle. The boat rips out of the hole and jumps to a plain but at full throttle the motor breaks up if i back down a little it clears up back down a little more it breaks up back down a little more clears up again. It acts the same way increasing the throttle at a slow rate. I have replaced the plugs, rebuilt the carbs and adjusted the timing Im not sure where to look next anyone have a clue?