Crankcase pressure test
by Had Robinson
Remove the engine from the frame and then remove the exhaust system, spark plug, cooling shroud, carburetor and redrive.
Plug the exhaust and intake ports with HD aluminum foil (like a gasket without the hole). Use the spark plug hole to pressurize the engine 6 -10 psi. A handy way to do this is to use some of the fittings of an engine compression test tool. Most of them have a check valve to hold the compression value so you can read it. It might take a little ingenuity to fit it all together so that it works for you. Use soap solution to check the entire engine for leaks. You will have to partially submerge the engine in water in order to check the front main seal for leaks unless you remove the cooling fan and flywheel (not recommended).
Pressurize the engine BEFORE putting it in the water. Water will not harm a coil in good condition. However, keep as much of the secondary wire as you can and the spark plug cap out of the water. You do not want any water in the spark plug cap.
Leaks will make the engine harder to start and can lean it out at the high end.
Replace any seals or gaskets that leak.