If you're sure fuel is being delivered I would say it's an ignition problem. I had the same shit when my battery was dying while driving (lack of sufficient ignition the same). I don't know a lot about what happened, but I figured the popping was from an unburned mixture of fuel/air that escaped the cylinder (from incomplete combustion due to weak ignition) igniting in the exhaust from the heat.

I think that might be happening with you. Somehow your fuel is not being properly burned. I could be wrong, someone correct me if I am...

While cranking, does it tend to sputter and die, or is there no give at all?

Did you replace the distributor cap or the capacitor/coil?