Andrew's 1990 Yamaha YZ125
The 1990 YZ125 was my first 'real' motocross motorcycle. I was not overly impressed with the overall power of the motorcycle when I originally bought it, but the powerband was amazing. No matter what gear you were in the bike had control for a few fast seconds.
After I did some work on the carburetor and cleaned the powervalve (very sticky mess, my first experience with a two-stroke as well) the YZ started to display a slightly wider power range and a little bit softer transition from off to on power-band.
I found the bike to be fast and fun on open fields and trails (I never rode it on a track) but inadequate for any kind of trail riding. The power range was too narrow for maneuvering any sort of tight or steep are on a trail.
After riding the YZ125 I could never go back to the soft forgiving ride or the ultra-wide power band of a trailbike. I had to have a motocrosser, even if I was going to ride on the trails. This is what led to the eventual purchase of my 1999 YZ400F.