You may have read previous posts concerning a real bad bogging problem with my 99 YZ400. After much time and work I have found the problem and repaired it. The bike works wonderfully now and makes my WR seem tame in comparison. What I discovered was that the intake cam had spun in the gear approx 20 degrees (40 crank degrees!), retarding my cam timing. As a consequence, compression was low and power output was horrible, plus it had a bogging/dying problem off idle. Though the timing marks on the cam gears were aligned with the top of the head at TDC, the intake timing was retarded 40 crank degrees. I reindexed the cam, heli-arc welded the gear on (exhaust as well)and it is good to go. Thought maybe someone else out there might be experiencing a similar problem. Thanks to those who posted suggestions and information.