Hi guys, I know this topic has been covered to death and I've read all the posts but still going round in circles trying to resolve this. Since I bought the bike it backfires when snapping the throttle shut from med /high revs. I've just reshimmed the valves and rebuilt the carb using the 6 sigma jet kit. The bike starts, ticks over and runs very nicely after much tinkering but I seem to be swaying between too rich (to the point of fouling the plug) to too lean where it back fires. There is also some bog when snapping the throttle open from idle but not noticeable on a ride (it just wheelies like crazy) It has a yamaha exhaust but I'm guessing it's from a yz as there are no baffles and no signs there ever was one? Airbox has been modded with side panels cut out. Carb is currently set with mixture screw 1 3/4 turns out, pilot jet is new from the kit, main jet is 172 (up from previous 165), needle is on second ring from top, leak jet has the blocking screw, and pump mod o-ring in place. I also have a 175 and 178 mj to hand. My question is, in what order should I make changes to the settings? I have tried so many combinations and now starting to lose my marbles!