Ok, backfiring solved!!
I replaced the exhaust gasket at the head, cleaned the inside of the pipe opening and exhaust port, replaced the Supertrapp with a HD Dyna muffler and made sure there are no leaks. Yeah!!!
It sounds much quieter until you open it up, then it sounds deeper and really nice. It also looks pretyy nice, especially with the 7" J C Whitney heatshield and I am happy with it.
Thanks again for all the great advice.
Ike