Please PM me with the location when you park the car (sorry I couldn't help it) I still would not rule out a lean condition on this, maybe not a ignition, I am no expert in this part of diagnosing without hearing type of thing but a pop under load can happen with a lean condition (especiallly when all the igniotion is not in question) could be a vacuum leak or even a to lean a carb, when it starts acting up choke it if its a manuel choke and if it clears up look for why its leaning out. Sure won't cost or take much to rule it out.