You can make a redneck leakdown detector easy. Just get a compression tester hose and and a air nozzel gun with a tubing extension. If you don't have a compression tester kit with a detachable hose you can even use an old spark plug with the porcelin broken off and a piece of tubing the same size as the air nozzel welded or brazed on. Now clamp a rubber hose between them the right size to hook them together. You'll probably need several hose clamps on each side to keep the hose from slipping off. With the rocker gear removed screw it into each cylinder and shoot air and release the trigger and listen for air escaping. The trigger will prevent it from coming back through the hose.
If air comes out the carb, you have a bent intake valve.
If air comes out the exhaust, a burnt or bent exhaust valve.
If air shoots out between the block and head it's a blown head gasket.
If air comes up through the motor out of the crankcase very quickly, like as soon as you shoot it in, it's going right by the rings or maybe even (rarely) a hole in the piston.
It's been my experience that most times low compression in one cylinder, if the cam checks out and the valves seem to all be opening and closing right, is a burnt exhaust valve from engine detonation or even a blown head gasket. It's rarely an Intake valve.
