I have a 07 trx400ex with a HMF exhaust and a K&N filter with outerware. Stock airbox with lid. I live in Texas so temps range from 25*-100*. I just purchased it used and the guy said it was jetted, it starts fine BUT as soon as you press the throttle it bogs, sputters and then it will take off. Revving it in neutral does the same and sometimes backfires till it gets past the 1/4 throttle and its then fine. I took the carb a part and it is very clean so my first thought that it was dirty was wrong. It has a 168 and a 38 jet. Fuel screw was at 2 turns out. I cut a groove in it so it can be adjusted easier. Should I jet to a 40, 42? and leave the 168 since the top end seems ok? What kind of jets do I need, I see b series, c series and I have no clue.