When it comes to racebikes, faster almost always is better, and that’s especially true with 250cc motocrossers. Since they don’t have nearly the sheer power of the big 450s, Lites-class machines can gain some serious advantages with even small improvements in engine performance.
Although Kawasaki’s KX250F has traditionally had one of the strongest engines in its class, Team Green’s engineers have managed to squeeze even more juice out of the 2013 250F. While they were at it, they also redesigned the chassis to make the bike feel lighter and more agile. I got to experience these improvements first-hand at the new KX-F’s press introduction at Spring Creek MX Park in Millville, Minnesota.
Improving the KX’s power output involved designing a straighter, downdraft-style intake tract and fitting it with a less-restrictive air boot. This arrangement makes better use of the KX’s dual fuel-injection nozzles, resulting in a jump in midrange and high-rpm punch. A new piston, which zips up-and-down in a shorter cylinder, works with a higher compression ratio (up from 13.5:1 to 13.8:1) and a redesigned headpipe to boost bottom-end performance. The new header features an acoustic resonator chamber with greater internal volume that aids performance while also reducing exhaust noise.
Most important is that all of these upgrades work as advertised. Good, usable power is always there, ready for action when the rider asks for it. I was even able to pull third gear out of a few tighter turns without bogging, something usually only doable on a 450 and impressive for a 250. When I helped it out by feathering the clutch a lot, it was tough on the plates. The clutch faded toward the end of a practice moto, and I even burned one up after just one day—something I haven’t done in years. More power, same clutch? I think a beef-up is in order.
For Millville’s track, which features some serious U-turns up and down hills, the gearing was a little short. The KX has such a quick-revving engine that I went through first and second gears too quickly. The bike now allows you to change the power delivery with DFI Map selector couplers (as on the 450F), but I preferred the stock setting; it gave the KX-F the most even spread of power from low rpm to high. The aggressive map made the bike faster but isolated the power so it delivered a lot of burst that focused more on the midrange. The Hard Terrain (mellow) map provided easy-to-use bottom-end power but didn’t allow good get-up-and-go when it was needed.
The aforementioned chassis redesign includes a new frame and swingarm as well as an upgraded SFF fork. The frame is 4mm narrower, resulting in a riding position that makes you feel more like you’re on a slim two-stroke. The flatter seat is nice for rider mobility, but the smaller fuel tank (down to 1.6 from 1.9 gallons) can have its drawbacks for anyone using a KX for other forms of off-roading.
Kawasaki made the chassis more rigid for 2013, a change that has its plusses and minuses. The inner fork tube diameter went up 1mm, from 47mm to a 48, and that also knocked a little flex out of the program. The shock, however, is on the soft side, pretty much just as it was on last year’s bike. The overall reduction in flexibility gives the bike a slightly more rigid ride; but while some comfort may have been lost as a result, the KX is more planted and predictable than it was in 2012.
In its as-delivered form, the KX250F was a little unbalanced for my riding style, and it took some serious seat time for me to tune it to my liking. To help cornering ability and balance, I had to take all of the preload out of the adjustable fork and then add five clicks of compression. The fork’s spring rate is too stiff, especially for a bike most likely to be ridden by flyweight teenagers. The shock was the opposite: I had to set the preload firm at 100mm of sag, with eight clicks of compression, go three-quarters in on the high-speed damping adjustment and one click slower on rebound. These changes made the shock stiffer and the fork softer, allowing the overall suspension to be compliant.
I was not able to spend as much time on the new KX as I usually do when testing a motocross bike, and I only rode it at one track, but I can tell you this: The 2013 Kawasaki KX250F is a more aggressive, race-intended motorcycle that is fiery fast and wants to be ridden hard. You don’t have to be a top expert to ride it; but if you are, you’ll like what it gives you.
