Verify the firing order and timing. Remove and inspect the spark plugs for fouling and cracked insulators. Look up inside the spark plug wire boots for traces of greenish discoloration or an accumulation of black soot. Remove the distributor cap and check for moisture, cracks, carbon tracking and rotor condition. With the engine off, look down the throat of the carburetor and open the throttle by hand while you watch for positive squirts of fuel out of the accelerator pump nozzles. Does the pop occur with the choke applied?