My question is will a Mercruiser 120 hp work with a Mercruiser 165 leg. The gear ratio difference is 120 = 1.98 and the 165 = 1.65. I have recently put a 165 leg on to a 120 hp. The boat is a 1975 Glastron 17'. It will not get past 2000 rmp at WOT. Should it? Will that much of a gear ratio make a difference. The prop that is on it now is a 19. i know i should got to like a 16 or 17 but why won't it open up when the the throttle is wide open? Is it a carb issue or a gear ratio problem. All I can get out of it is 20 mph and it takes forever to get there.