These motors have a metal pump impeller which is good because it doesn’t usually wear out.
They also have some somewhat constricted water passages in the cylinder, so if you haven’t already done so, make sure that compressed air can flow freely through the cylinder. Blow air in both directions to make sure any rust or mud flakes get broken loose and blown out. In some cases, the cylinder needs to be soaked in hot water for a couple of hours too soften/loosen up silt or other deposits that have dried up and hardened in place. some of these motors have aluminum cylinders, and in those cases the cooling passage is made up of a copper tube that is wrapped around the cylinder liner then aluminum is cast over everything.
I once had a Ranger that wouldn’t move enough water to cool at all well. The cause was an obstruction in the water passage that took me about two hours to clear out by pushing a length of heavy wire into one water port and lubing it with WD-40 while heating the exterior of the casting with a propane torch. Eventually I got the rust/mud ball that was in there to break down to the point that compressed air could finally blow it out.
Good ole “Ranger Dave”. He got that name because as received he was painted up in the colours worn by Super Dave Osborne (Or Evel Knievel, whichever you prefer). He was a bit of a joke of a motor, but I did get on the lake with him once.
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...