How repetitious is the pop? You can tell simply by doing this. Start it up. Drop it in drive with the parking brake fully applied and your foot on the brake pedal firmly. Ease into the gas and bring the rpm up against the converter holding the car still. If you get a pop with every cylinder fire, like pop, pop, pop, pop at even intervals, you have an exhaust valve that's staying closed "somehow". The most common thing is a flat exhaust camshaft lobe, although a bent pushrod, collapsed lifter and broken rocker can all do it as well. What I would do is remove the valve covers and start the engine. Take note of how far each rocker arm opens and closes and look for one that's either not moving or moving much less than the others. A compression test will not spot it, as the exhaust valve is remaining closed and the cylinder is still firing. It is firing exhaust back up through the intake and out the carburetor, instead of out the exhaust port and through the exhaust manifold. This is why it not running well. The exhaust firing back through the intake tract is disrupting everything.
