When I bought my used '06 WR450F, it didn't want to idle. It wouldn't react to the fuel screw adjustments so I went up on the pilot. I ended up with a 52 which is quite rich for where I ride (sea level) if you compare to what everyone else is using (usually a 48). Bike was still hard to get warmed up and had a rough idle. One day, I noticed the idle improved. I ran it like this for two years. Last month I removed the carb to install an adjustable leak jet and noticed that the tip of the fuel screw was gone!!! I had remembered that the screw had vibrated loose one day and was resting on the starter. That's probably when it broke off. (yes, the bike did stall). This was the aluminum aftermarket thumb screw. All I had was the oem brass so I put that in. Bike did not want to idle. Sounded very lean. Leak jet was set at #40. Obviously it was working fine with the broken off nipple on the fuel screw so I grinded that off the oem part, put it in and the problem was solved. This makes we wonder though why my bike is so lean on idle to need a fuel screw setting and pilot jet so rich. I wonder if I should up on the pilot again to where I can get a new fuel screw to work? I suspect a 54 or 56 pilot might be necessary. That is abnormal for a WR down here.