It backfires out the exhaust w/ a very very knowledgeable race buddy says could mean very rich running. That might explain why it happens more when warm. Backfiring out the carbs would be more likely an ignition/electrical issue. The carbs did have some rust scale in the strainers from and I'll check the sparkler pluggies for color. The Summit Racing tech support guy said to go w/ the digital ignition module, and the requisite heavier plug wires and coil. I might to that anyway just to be modern.