drivability issue

hi there again everyone,
i got another problem i just thought i would throw it out there and see if anyone had any suggestions. i am driving a 318 dart, just shy of 10:1 compression, its got a descent little cam 484 lift 284 adv duration, linked to a manual trans in an a body. its a fun car for a daily driver, but thats besides the point. my problem is either with ignition or carburation. it was running fine one day then it just died. weak msd box :-(, i then replaced the msd with a crane ignition, and took the carb off and took it appart to clean it up a bit and change the jet size, 2 sizes richer. its a road demon jr. carb by the way. jet change really helped the cars throttle response and power, but im not sure if i messed something up cuz now the only problem i experience is a backfire and pop at around 2800-3300 rpm only under light throttle, like a cruze condition. under a hard accel though it runs fine through the rpm range. i dunno if i maybe i didn't do something right w/ the carb, or if its something like timing or ignition. if anyone could shed some light on this it would be greatly appreciated, i wanna get back to cruizin around in my muscle mopar! :-) thanx