Get the valves closed on one cylinder at a time, put the transmission in gear and chock the wheels, and put air into the cylinder with the blow gun through the spark plug hole. Listen for leaks at the crankcase, carburetor, and tailpipe, and look for bubbles in the radiator. It's better than a compression test for finding leaky valves, rings, or head gasket problems.
Back off the valve adjusters half a turn each to be sure they're not too tight before doing the leakdown test.
Jerry
