Backfiring Back Through the Carb

[cgrossl]

I have an 85 SWB Chevy, 2wd with a 305 and a TH350C. Over the last couple of weeks, it has developed a problem with backfiring back up through the carburetor. The engine is original with a Q-jet on it. It has about 135,000 miles on it. The Q-jet has been replaced at some point with Holley reman unit. I rebuilt the reman carb again last winter. It has been fine since then. The backfiring occurs mostly after the engine is really good and warm. It happens as I am squeezing on the gas pedal, like when pulling out or giving it more gas to go up a hill. Sometimes it is pretty bad and sometimes it doesn't do it at all. Timing, plugs, plug wires, etc. are all good. For some reason, I want to say that this is ignition related, but I'm not for sure. I've never seen a carb issue be this intermittent. Any suggestions?