The old 4hp needs a rebuild I think, I've got all the ignition parts, I've replaved them befor seems like low compression?I can turn it over with my hand? Do I need rings, do i need oversized 10 or 20 piston? is it valve lash? it runs for 5 min then just stops, and had no power, (1973) is this something I can tackle do I need a machine shop? It's one of these I get parts when I can get up some money?