20 hp mariner surging at speed

[sherick007]

Hi, Everyone<br /> I have a 1987 20 hp mariner on an 18' Sylvan pontoon boat. I have 2 questions.<br /> 1.when you open the throttle it never seems to get near peak rpm's even though the butterfly in the carb is opening all the way open.<br /> 2.When you are running along at cruising speed, it will run at the top speed that it does reach for 30 sec. to a minute, then it drops in rpm as if you pulled the throttle back to 1/2 for about the same period of time and then it picks up rpm again. It will do this repeatedly until you run out of lake.<br /> Any help would be greatly appreciated,<br /> Thanx,<br /> R.J. Byrnes