I was just wondering why Yamaha chose to produce a 400cc bike when they came out with the YZ400. It is my understanding that AMA rules were changed to allow 450cc bikes to compete, so why didn't they just start out with a 450? Also, was there any significance to using a displacement of 426cc in 2000? 426 is such a strange number - historically I thought most motorcycles manufacturers just round off the number to something even. Pardon my ignorance, I'm just trying to learn the history of my beloved toy.