The info from Edelbrock states, in part:
These cams are for high performance street use only and are not for heavy vehicles. Use with Edelbrock or other aftermarket cylinder heads, adjustable valvetrain components, and at last 9.5:1 compression ratio. Headers, high energy ignition systems, lower than stock rear end gearing, and a high performance torque converter in automatic transmission equipped vehicles are necessary to gain all of the performance in these camshaft kits.
If this wasn't followed, then you cannot expect the cam to work as it was designed to.
That said, there's no reason- even if the engine is bone stock- for it to be backfiring through anything, be it carb or tailpipe.