They are not cheap, but if you purchase a supertrapp muffler, you dont need to rejet unless you use over 8 discs.  you will have no more backfire, a great sounding motorcycle and twice the performance. dont forget to add a free flowing air filter like the K@N.

I bought my Supertrapp from another member, and they do show up from time to time if you can wait.  New they are about $300 give or take arm.

The trapp is a little different, you add disks to reduce back pressure.  More disks more sound as well.  So if you get a supertrapp and your sparkplug suddenly goes super rich, add a couple of disks and it will lean it out.  Or vice versa.

When I put mine on, my bike was stock and it was perfectly tuned with 8 disks.  I went from a 145 jet to a 150, added 2 disks.  If I put on a K&N air filter, might need to add 2 more disks plus maybe another rejet.  Comprende chica?