Help. My bike has started to stall when I decelerate, especially when I disengage the clutch to downshift at slow speeds. It starts easily and idles great while standing still. Acceleration is strong. But when I slow down nearly to a stop it stalls. If I leave the clutch engaged it sometimes backfires and restarts. It developed this bad habit over the last 5-6 rides. I have changed nothing, except to adjust the pilot screw during the past 2 rides attemtpting to correct the problem. It seems to improve when I use a leaner setting on the pilot screw, but still stalls sometimes. I'm running a '99 WR400 w/stock exhaust and cam timing, grey wire cut, throttle stop removed, air box cover removed.