Poppin / Backfiring at low speed

[Shooter Mike]

I'll try to explain this as best as possible. Picked the bike up yesterday from a private seller
97 Suzuki Marauder 800
15,600 miles
Cobra slip-on exhaust

At higher RPM the bike runs well. I live on a military base and the speed limit is between 20 and 25 on the whole base. At this speed (and if I had to guess, I'd say the RPM is around 2200) there's a good bit of popping. When cruising, and I let off the throttle completely and the throttle is closed, I don't experience the popping/backfire.

I have a few idea's but would rather spend a few hours fixing it, rather than a whole weekend trouble shooting it.

My first thought is carb synchronization.

My second thought is that the carbs are not jetted for the aftermarket exhaust. I tend to think this may be part of the issue but not whole issue, simply becuase the it doesn't pop when the throttle is closed.

The bike starts easy, and idles fairly well.

It would seem as if it is a low speed circuit problem, but truth be told, I'm not familiar enough with motorcyle carbs to isolate and fix this issue without consulting someone who knows more about bikes.

The reason I'm leaning more towards carb synch is because the RPM at which it pops, and the fact that it doesn't do it on decel with the throttle closed. At a low RPM, the vacuum is the same on both sides of the carb slides. If one isn't delivering as much fuel as the other (out of sync), this could very well cause a mixture difference between the two cylinders. Those are my thoughts. I'd like to hear yours, so hopefully I can get pointed in the right direction.