m2100 carb issues,

Hi all, Newbie to the forum but decent hack mechanic here. I got a 82 cj8 that im slowly rebuilding and recently added an m2100 carb. Got it off craigslist, he got it from the "ebay guy". Still in the box but looks like he must have had it in the closet for awhile, had a "hotmail" email account for contact info if that tells you anything. My problem is that no matter how i adjust it, change the mix or timing i cannot get it to stop an exhaust backfire when i let off the throttle. I did the ford cap and plug conversion to try to burn up the excess gas with an m2 blaster coil but still nothing. Double checked for throttle body leaks. Got some emmissions on it still so im wondering. Can i have the emmissions hooked up incorrectly or do you think its a better bet that the innards of the carb are dried out and i just need to rebuild it. Could it be a nutter bypass issue, i know technically thats not needed till 83 but... Need to do emmissions but dont know if it will pass with the backfire. Thanks for any help.