Yesterday got a BF100 project motor running finally. Picked it up used with supposedly no spark. Found the kill switch was grounded and put a new set of points in and fired right up. Had it in a 55 gal barrel and would idle great, run up and down on throttle and back to idle no issues. Good water from pee hole. I let it run at 1/4 throttle (hood off) for about 10 min. At 4-5 min warm water out pee hole, at 8-9 min hot water from pee hole, and at 10 min the aluminum housing/oil sump was hot. Hot enough that it couldn't be touched. Motor does sound a little loud on the exhaust end like it could have a leak but nothing I could see. The hood hdid have the metal plate that says 4 stroke removed and two 3" diameter holes drilled in its place from the previous owner so I am sure he had overheating issues also and wanted to vent it with the holes.
Besides the thermostat what might be the cause?
Besides the thermostat what might be the cause?