one "bank" popping is more than likely ONE cylinder and could be as simple as one plug wire is loose or bad. it's highly unlikely a muffler is causing it. The car is running very, very rich as evidenced by the condition of the plugs you removed. You need to get to the bottom of that but, a bad plug wire or plug would cause it to pop. Tell me how I know.
Buy a $50 standard ignition products plug wire set and cap and rotor and replace all the plugs. Start there. then tune the carb mixture. basic stuff to see where you are then.