1969 ford f100 backfiring through the carburetor, any ideas?

It has what is believed to be a 390 small block with a 4 barrel holley carb. When in any gear if you give it to much gas it spits and sputters and backfires through the carb. It started shortly after putting a new exhaust on it, I don't believe that would cause it but i could be wrong. Any ideas are welcomed.