My bike will let out one to two backfarts during the decell process. I recently purchased the bike and the previous owner put less then 100 miles on it in the 3 years he owned it. Not sure it that has anything to do with it.
It the bike is all stock then the backfire on decel is normal. The bikes come from the factory set to run on the lean side to meet EPA specs and when you let off on the throttle you cause a overlean condition which causes the backfire. Do a search on here for how to adjust the idle/air mixture screws and you can eliminate most if not all decel backfire.
Id run a good fuel cleaner threw it seafoam or stp somthing of that standart. 100 miles n three years that bike sat alot so fuel more than likely varnished. Wich would cause clogging in the slow jet aka pilot jet. The bikes stock settings are very lean so i also agree that the fuel screw should be turned out atleast a 1/4 turn.
03 750 ACE
05 vlx bobber (the wifes)
06 FLHXI Street glide
1980 kz750 bobber/chopper (project)
The small things are what make the biggest differences...