710 backfiring/ stalling

[Hawkeye Pinz]

I suddenly started having a problem with my Pinz right after taking off in 1st or 2nd gear. It idles pretty good then starts to sputter and lose power when I take off. I've also noticed a kind of backfire coming from the exhaust. It's not a loud bang or pop but kind of like a cough or snort. I run Pertronix so it can't be the points. Maybe a carb or timing issue? Thanks in advance for the help