I have a 1984 50 HP 2 cylinder Evinrude. The 40 ,50 and 60 HP engines are all the same bore and stroke. The books that I have shows no differents in part numbers for the carburators, intake,reed plate of the 50 and 60 HP. The exhaust parts also are the same. Does anyone know what was done to increase the horsepower from 50 to 60. In the 9.9 hp a simple carburetor change from the 9.9 to the 15 worked great. I can't find the difference in the 50 to 60....Help