Thanks for the reply’s. I checked both cylinders with a borescope and they look clean. No excess carbon buildup on the pistons and no visible oil. The compression is this high with dry cylinders. The 1973 18 and 20 hp motors used the same head, but the 25 is different, according to MarineEngine.com. The head has definitely been replaced but I do not know if it is the correct one. It is possible it is a 18 or 20 head. I don’t know what the difference is. I checked with my old compression tester and got similar readings.
