Random Backfiring

[brielly]

I'm at my wits end trying to figure out this problem. After installing customefis muliport kit I was getting a lot of backfiring through the exhaust. John at customefis decided that a vehicle speed sensor would help resolve this problem. This seemed to work. I drove around quite a bit today with no backfiring. I stopped at the mall and when I restarted and left it back fired like crazy when letting off the gas in 3rd gear. After my next stop and restart there was no backfiring all the way home. What could cause it to backfire sometimes and then run perfectly other times?

[475thFG]

I've had champion plugs start going bad and do the same thing. Spent $400 on a head job (in 1982) because of it. I'd start there, 'cause it's cheap. If that doesn't do it, you might pull your O2 sensor (it does have one, right?) and heat it up with a torch and make sure it's working. Other than that, I simply don't have a clue.