It looks like I missed that little detail. Pulling a cylinder head can actually hide the source of a minor compression loss. Putting air pressure into a cylinder through the spark plug hole with both valves fully closed and the crankshaft locked by putting the trans in gear and setting the parking brake or chocking the wheels can pinpoint the leak. Listen at the carburetor, tail pipe, and oil filler cap to see what's leaking, and do the same thing for every cylinder. Bubbles in the radiator indicate a head gasket leak into the cooling system, or maybe a cracked head or cylinder wall.
If you set the air pressure to 100 PSI with no air flowing, the pressure the cylinder is able to maintain translates to a "percent of leakage" measurement. 90 PSI = 10% leakdown, etc.
Jerry
