Yoyo,
just had the same problem with my bike as well, running rough and backfiring at slow to mid range speed,took it to crew for Suzuki to look at and they said it was due to a damaged valve exhaust seal , the throttle bodies being loose and fitting an aftermarket air filter,
also had the tank cleaned and a new fuel filter fitted.They then ran the dyno test and did a bit of re-mapping. Now runs sweet as a nut, hope this helps in any way.