Hi there. I am sure you guys on here will square me away pronto. Here is the problem. I have a 2004 YZ450F. Bought it a month ago. If I increase the idle, by turning the idle screw, it goes up for a couple of seconds, then drops down to a slow idle again. If I blip the throttle it sits at the higher idle foe about 5 seconds then drops down again. Any ideas ?