Depending on cranking speed, you should get compression pressures at, or near, 100 PSI. It will start and run at about 85 or above. Here's another method, using air pressure, if it's available. Get the piston on the cylinder you want to check at Top Dead Center (TDC)on the compression stroke (both valves closed) and lock the flywheel by putting the transmission in gear, and setting the parking brake. Put air pressure into the cylinder by brazing a fitting into a discarded spark plug shell and attaching the air hose to the cylinder. Listen for leaks, at the carburetor, exhaust pipe, and oil fill. You've just checked both valves, and the piston rings, for leaks. More than a small seep indicates you've got a stuck, or burned valve, or bad rings. (or too-tight valve clearance).
Did you install new spark plugs, and are they firing?
Jerry
