I have purchased a 2000 WR400F that is real clean. The guy that I purchased it from stripped it right back removing all the road gear and putting a YZ tank and plastics on it. I also own a 2003 WR250F. Every time I ride the WR400F it shakes the hell out of me and tends to get really bad headshake under heavy throttle over bumpy track (on the local race track). The 250F handles perfectly and does not have these issues. I can jump heaps further on the 250F and do much quicker lap times. I am wondering if the headshake is most likely caused by the suspension setup? Maybe the rear shock is too hard or the front forks are set too hard. I am looking for some responses on if this is a known issue with the 400's? Getting off the 250F, I felt fine. After riding 2 laps on the 400F I had to stop as my shoulder was acheing and my hands were cramping. I have never had to hold on so tight in my life. Any thoughts on why the 400 would be handling so bad? It corners fine, and pretty much the same as the 250F. It is just over bumpy stuff at speed that it gets bad shake..