I have a 2000 WR400. And like a lot of them as it seems, when I whack the throttle open from low rpms, it justs wants to die. I have read many of the post on here about the BK mod and thought orginally that maybe that was my fix, but after looking into the problem, I think my problem is not too much fuel from the accelerator pump but not enough. I removed the subframe and watched as I opened the throttle quickly (engine not running) and noticed that the squirt (more like a dribble) was relatively weak and not very long. So after putting it back together, I started it and manually operated the AP by pushing the linkage down with screwdriver at the same time I opened the throttle and it reved with virtually no bog or stumble. Do the springs in the AP get weak over time? Is there something I can do to fix the AP problem. Any advice would be greatly appreciated.