I have a 2007 YZ450F and every now and then it tends to hang a bit on idle. When I start it cold with the cold start knob out the RPMs are about 2500 and when I blip the throttle they rise to about 3600, which is good for knob being out. But the real problem (so to say) is when it is all ready warmed up and it sometimes (not always) hangs for about 5-8 seconds before dropping to it normal idle(about 2000RPMs). The temp is now about 32 degrees Fahrenheit ( zero celcius) and elevation is from sea level to no more then 700 ft. Jetting: 48 pilot with 1 turn out 165 main all else is stock. I am not sure if this problem is related to my hanging idle, but this bike tends die in corners more often then my old 2004 did. I can`t say it is due to too low RPMs, it like it doesn`t have the power to run or something. It could be just me, however. One more question. What up with the valve thingy attached to the hose coming from the fuel tank cap? I think I heard that it tends not to work as it should(vacum).