The YZ400F had a motor too good for it's shitbox chassis, the japs should have used the Husaberg chassis as well as copying the engine-same bore and stroke as 400 Berg, same type of piston design (no skirt ) to produce a fast reving lightweight 4 stroke engine. The japs have always copied the Euros and most of the time made it better! That first 400F put a lot of people in the intensive-care ward, as bad as any 3 wheeler. The story I heard was Yamaha bought a 501 Berg and a 400 Berg to see what made them go so fast and the rest is history!