I have just obtained a 1982 9.9hp rude that runs great, and a 1979 9.9 that doesn't. On the '79 it has sat in a basement for years on its side. There is very little compression if none. We took the head off and the exhaust port and it all looked very clean and no scoring on the walls. The flywheel can be turn very easily by hand with the plugs in. I was thinking about rebuilding in my free time and also about putting the 15hp carb on it. My question(s) is what could be the problem with the compression and would it be worth the 15hp carb?
by the way the rings are free on the pistons.