I finally broke down and bought the JD jetting kit for my '05 WR 450. After installing the Blue needle in the 4th position I figured I'd better check my main jet and make sure it was right for the new needle. I was shocked to find out that the main jet was missing . Since my last jetting change I've done two play rides (one was over 100 miles), raced two desert races (one a National Hare & Hound) and I never would have guessed that my bike would run as well as it did without the mj!!!! I musta left it out and just put the float bowl cover back on. I was having a slight pop/ bobble when I was running at 1/3 throttle and figured I'd give the JD kit a try to solve the problem. The funny thing is I've had the two best races of my life riding a bike witout a main jet!!!!!