If the compression test shows low or zero compression, and you have an air compressor there's something else you can do to check valve sealing.
Pull the valve cover and remove both rocker arms on the cylinder in question.
Take the hose from your compression tester and take the check valve out, then screw it in and hook it up to shop air.
Then if you hear air moving, listen at the carb, exhaust pipe, and oil fill.
If air is coming out the carb, it's an intake valve
If it's coming out of the exhaust it's an exhaust valve
If it comes out of the oil fill, you burnt the rings or piston and will need a rebuild.
1973 VW Karmann-Ghia first car
2009 Challenger R/T 6MT, Flowmaster, inTune daily driver
1977 CJ5 304, 3MT - under construction
And many in between!