I have an '01 CR250 engine that runs great. But it doesn't seem to have the bottom end of a new YZ engine. Does anybody know which of the '92 - '01 CR250 cylinders has port timing (and power characteristics) most similar to a current YZ250?
My 87 has some good bottom end, maybe you should consider riding one of those. The bottom end is like riding an XR400. The top end is like riding an early 4-stroke motocrosser. It's an interesting engine.
Of the '92-'01 cylinders, the '99 has the best stock porting for strong bottom. They do tend to run flat up on top though. I had to short-shift to get the most out of the motor. It was very good for the trails and for hillclimbing.