Andrew's 1999 Yamaha YZ400F
The YZ400F is the way high performance dirtbikes should have been made from the beginning.
Four-stroke power in a motocross frame with the weight to match. Moving from a 1990 YZ125 to this was certainly a BIG step up and somewhat of a challenge as well as a relief.
The YZ400F is certainly heavier than a 125, and it's a little heavier than most motocross 250's, although once you get used to it you barely notice.
My first time out I could feel the weight beneath me, it took a little more to move the bike around while riding. It is not noticeable when you go down and need to pick it up again (I'm pretty sure adrenaline plays into this somewhat).
Riding the 125 on trails was always a challenge, preparing for steep hill climbs and negotiating more technical sections at low speed were always interesting.
With the power of the 400 I can put power down instantly (just like a 2 stroke) but it's there all the time in a nice constant flow, no powerband to worry about, it's just like always being on the powerband.
The throttle response is phenomenal, instant reaction to any movement in the wrist. All I can say is that this is one heck of a bike. If you want motocross performance with 4-stroke power (and can deal with a somewhat finicky beast to start) The YZ thumpers are a great way to go.
Here's what Yamaha had to say about the 1999 YZ400F.