Here's some info to correct the lean condition many of the 800's have "out of the box" that causes the "sneezing" and "backfiring", especially when cold. It was extracted from info by Richard Fisher : You can use the factory needle and main jet (#135) with pretty good results if you will put a 1/16 inch shim under the needle (raising the needle), and reassemble the slide assy. Next, pull the idle jet air plug (the little plug that covers the adjustment screw) near the rear of the carb bowl) and back it out to about 2 1/2 to 2 3/4 turns from bottom ( factory set on mine was 3/4 turn!!). You will get results very similar to the Cobra jet kit but not quite as progressive from idle (according to others who have experimented with aftermarket jet kits). Using the Cobra jets gives a more progressive needle to jet ratio. I did this with my stock pipes and intake, and it made a WORLD of difference in the bike's performance! This is especially important if you've gotten rid of the stock exhausts and have gone to aftermarket stuff that flow well like Cobra or Vance & Hines. Always do the jet mods before the exhaust pipes are installed if you don't want the infamous blue pipe experience, (non-reversible).