I have a 1984 4 cylinder 50hp mercury, I had problems with the carb that turned out to be the float in one of the carbs was bad so I changed that out. I also put a new water pump and new front and rear sills on the lower unit. After changing these all of these out I've had problems getting to motor to run right. It get full rpms when I have the muffs on it but when I put it in the water and try to put a load on it it won't build rpms at all. I also changed the spark plugs so I know its not those. Can anyone give me an idea as to what it might be?