soot

Have voo doo full exhaust and morleys jet kit. Have soot on the tips of the exhaust and when im running at high speeds and let off the throttle getting some backfire. What do I need to adjust? thanks

I recently installed the UFO 4 into 1 Dragstar on my Max. The bike is new, about 300 miles at the time of this message. The carbs have not been touched, no jet ket. The bike runs great too. I ran my finger inside the exhaust tip and got black soot on my finger. Like I said, the bike runs...