318 issues

You said that you checked the compression. Did you also do a leak down check? Since you said you have popping out the carb I keep going back to the valve train. It almost sounds like you might have a sticky valve or something causing a valve to hang up. Are you sure all the valves are closing and sealing properly? I know engine issues can be very frustrating. Just don't rat hole yourself. Make sure you cover all the bases. Good luck in finding this "demon".