Most seem to agree the backfiring in stock condition is a result of lean carburetion.  Richening by needle position / jet changes helps, but not completely.  Here’s another theory to implicate the stock muffler.  Installation of a better flowing muffler like the SuperTrapp eliminates most, if not all, of the explosive booms with no other changes, even though it tends to lean the running even more.    So a lean condition per se is not the sole culprit.  My guess is the stock muffler is so restrictive it traps unburnt lean mixture long enough for it to ignite later (backfire).   A better flowing muffler exhausts this explosive mix sooner.  If so, how ironic that to meet noise restrictions Suzuki make a muffler actually promoting sonic booms far exceeding the dB standard!

For what it's worth.... You don't state your mileage. It took a good 3.5k miles till my exhaust actually started sounding decent. What happened? I don't know. Burned in? Conditioned? But the Backfiring, at least the little that remains, seems to be just from the exhaust loading up. Does it need "tweeked"? Sure. Will I? Absolutely. I just wanted to point out that new "muffs" need some time to get conditioned to their real Purr.

I'll second that!  Put a SuperTrapp on and you've got a whole new bike. Jekyll and Hyde so to speak.  This is the way it was meant to be.  Hard to put in words but the quality of the ride is where it should be and reminds me of the old pre-EPA days of my Velocette and Ducati singles.  The sweet song on over-run (engine braking) is a treat to the ears.  Burble-burble, pop-pop!  Go for it!