[Buzz]

Hi guys. I fired up my Cobra today for the first time since the rebuild began 8 months ago. I'm running a 383 Chevy stroker with a Holley 750 on an Edelbrock Contender intake. The ignition system uses a ballast resistor with a Mallory Unilite distributor. Before shutting down to rebuild the car, the engine was a only little bit testy to start and ran beautifully. The body off rebuild was mostly suspension, brakes, interior, exhaust system and a new wiring harness.
Now, the engine starts real easy, sounds healthy and revs smoothly for the first few seconds and then develops a consistent backfire at idle. When I rev, the engine sounds great and the backfire stops but returns at idle and seems to get stronger and louder the longer the engine runs. Nothing has been changed in the ignition or fuel system except for new spark plugs and wires and of course the connections for the new harness. I also get the occasional flatulent sounding backfire through the carb when it returns to idle after reving.
I NEED HEEEEELP!!!
I ran a search on backfires and most problems stemmed from exhaust leaks on deceleration - nothing about backfires at idle. Any help will be greatly appreciated.