A couple of comments, if anyone is interested. Purchased my '06 WR450 in Sept 2005. Dealer did the air box mod, throttle stop, and removed the stock exhaust insert altogether, as well as a 'barely' street legal kit (mirror, horn, license plate). I didn't worry about the grey wire mod, nor have I jetted the bike.. I ride anywhere in elevation from my house @ 4600 ft up to 9600 ft. on a weekly basis.. and the temp. difference is quite large in the summer (50F to 95+), so I am not quite sure about what I would jet my bike to (recommendations are always welcome). Anyway, a few months after purchase, I put in the promoto billet exhaust insert to save my ear drums (and sometimes wear 'light' ear plugs when I ride). There is a noticeable difference in power, but my hearing is worth it and the bike still has plenty of power for my riding style. I am considering the AIS kit, but really, I am not bothered terribly with the popping on deceleration... it's a afterthought mod if you ask me. One year later, I still love this bike. Yamaha makes awesome bikes!