The Yamaha YZ250F has been refined since its debut in 2001. The result is a lighter and more powerful dirt-eating machine.
The bikes remained fairly stock throughout the shootout, with the only change a switch to different jetting. Honda's Eric Crippa has been experimenting with the jetting on the smaller CRFs and now goes with a slightly richer pilot jet (from 40 to 42), and turns in the fuel mixture adjustment from 2.25 turns to 1.5 turns out. As for the stock tires, the Honda comes with Dunlop's new intermediate/soft terrain tires, the 742/756 combo; the Yamaha comes with Dunlop's Intermediate/hard terrain tires, the 739s; and the KXF and RM-Z both come with Bridgestone's 601/602 intermediate/hard terrain tires. Unfortunately, the Suzuki RM-Z we had for testing looked like it had quite a bit of time on it and had non-standard Michelin tires and an aftermarket seat cover installed. Because of this, and the fact that it is the same bike as the KXF, we basically used the bike for photos and had the test-rider evaluations reflect the performance of the Kawasaki.
As mentioned earlier, Yamaha has had a four-year headstart on the competition when it comes to 250cc 4-stroke MXers. Since 2001, Yamaha has refined the YZ250F to make it lighter and more powerful, and this year was no different. It couldn't just sit back and relax with three bikes looking to steal market share in 2004. To make the bike lighter, Yamaha went with sweet titanium footpegs along with a titanium head pipe, and both brake calipers are also new and lighter with aluminum pistons.
The YZ250F has good power on the bottom end but is most impressive in the mid- and upper-ranges.
Suspension-wise, the bike now has a 48mm (2mm larger) Kayaba fork that features a special coating to reduce stiction. This fork design has abandoned the rubber-bumper bottoming system in favor of a more conventional hydraulic bottoming system. The patented five-titanium-valve head design is, of course, unchanged, but the motor did receive larger cutaway section between the cylinder and crankcase in an effort to reduce pumping loss and increase midrange performance.
We always thought the YZ250F had great midrange and top-end pull and now our suspicions are confirmed since we have some other benchmarks to compare it to. On the track, the little Y-Zed has decent bottom end, but it really comes on and snaps right through the rest of the powerband. Some test riders think it goes through its powerband too quickly. Test rider Dennis Ewing had problems with the power on a few jumps where he felt he would have liked the motor to still be pulling, instead of going sort of flat as he reached the face of the jump as the motor reached the rev limiter rather quickly at a screaming 13,500 rpm. At the same time, the snappy powerband was appreciated by testers on obstacles located right after corners.