I have a 1978 200 hp Merc. I was cruising at about 30 mph when the motor started to rev higher, but the boat slowed down. I could get the boat to go about 2-3 mph at about 1,000 rpm, but it wouldn't go any faster at higher rpm's. What is the probable cause of this?
My thoughts are for you to inspect the bottom end. Start with the prop itself.Make sure its not stripped on the splines, and the hub is ok. If that is ok, go to the gear assembly. Last and most likly least would be the driveshaft.