OK sorry for asking this all you pros probably get sick of answering it but here is my scenario. 1996 savage 13.5k miles hollowed/rammed out OE exhaust.  mainly iride between 4000-8500 ft elavation. i live at 8500 ft i ordered a sportster exhaust and think im ready to attempt the carb mods i have oe airfilter with modified door. Honestly i am perfectly happy how the bike is running now it only backfires like 20% of the time turning it off and when decelerating and performance is fine. with the sportster exhaust is it critical to do the spacer mod and rejetting. I love the really loud exhaust is the sportster muffler able to be modified like gutted?what exactly would each improve. i'll have to wait about a week before attempting since i just filled up today. also what plug do you recomend i think since i only have one i need the best. so what is the best?  thank you very much for all your help people!