I have a new 06 yzf450 and had a very lean condition, popping, backfiring etc... at zero to 1/4 throttle opening. Dealer stated they installed 45 pilots on all new 450s. They left the stock 42 in my bike. This is really no big deal, just need to do some minor tuning. Location is Charlotte, NC 795 feet above sea level. Weather has been in the range of 70 to 85 degrees and mostly dry air conditions. To correct the lean condition: 1) Installed a Boyesen QuickShot. 2) Tried a 42, 45 pilot and ended up going to a 48. The 45 was close, but the 48 makes the starting smoother (one kick) 3) Fuel screw 2~2.5 turns out (this is just my base line setting) 4) Needle raised (lowered clip one position) 5th clip position from top. 5) OEM - stock main jet 165 6) Leak Jet #50 (have a 45 on order and will update the post when I have the opportunity to test it) 7) Adjusted the accelerator pump timing screw .080 inch (Boyesen suggests .100) here is a good link for the proper steps to check the distance/timing. http://crfsonly.com/reviews/apc/apc.php This produces instant crisp throttle response, no hesitation, bogging or popping and one kick starting. Also there is no popping or backfires on deceleration entering corners. So far this bike is flawless, jetting is not a defect. This bike would run perfectly stock in southern FL 90 degrees 100% humidity. Suspension is super plush. Motor runs like an electric motor now, perfect.