The 2010 Kawasaki KX250F features engine and chassis updates all in an effort to get you around the racetrack faster than before.
In the ultra-competitive realm of 250F motocross racing every second counts and sometimes the brand of motorcycle can be the difference between winning and losing. That’s why manufactures tweak motocross bikes each year in an effort to put you out front. Last year’s KX-F received a complete makeover from the wheels up (read about it here in our 2009 Kawasaki KX250F First Ride), so for ’10 engineers focused on tweaking its existing platform, giving us the 2010 Kawasaki KX250F.
The new quarter-liter KX-F sports a host of changes to both its engine and chassis enabling you to scoot around faster than before. Perhaps the biggest news is that the new KX250F will not be equipped with electronic fuel-injection. Instead it’s fitted with the same mechanical 37mm Keihin carburetor as last year.
Although it looks virtually the same, the engine sports different cases designed for increased durability. Inside, a new piston slides within a 0.5mm taller cylinder that uses new cylinder bore treatment for smoother action. Not only is the piston lighter, it’s taller, hence the reason for the taller cylinder, and the 13.2:1 compression ratio remains the same. It also utilizes a shorter skirt and a much narrower piston pin area. Kawasaki claims these updates allow the engine to rev faster and harder through its 13,400 rpm range. Although the engine’s four-valve DOHC cylinder head remains the same, the intake camshaft holds the cylinder decompression on longer allowing for easier starting.
Looks can be deceiving. Although it appears unchanged, the 2010 KX250F employs engine and chassis updates for improved performance and durability.
The engine’s bottom-end received durability updates in the form of a longer crank pin and wider connecting rod and bearing. The lubrication system was revised with a more efficient oil pump design for increased oil flow and decreased mechanical power loss. The five-speed transmission received some attention in the form of revised input gears. Lastly, a lighter, narrower chain transfers power back to the back tire.
The exhaust pipe was also reworked with the header now fabricated from stainless-steel rather than titanium. Its front section is over an inch longer while the mid-section has been shortened by an equal amount. Also, the muffler now connects to the subframe via a less-rigid rubber mount.
Similarly to the ’10 KX450F (read all about it in the 2010 Kawasaki KX450F First Ride), it gets larger aluminum radiators that use a less-dense fin core to help prevent debris from getting lodged in them. The radiators are also stronger which allows the reinforcement brackets to be done away with.
In the chassis department, the KX250F’s twin-spar aluminum frame’s steering head has been engineered for more flex, thereby delivering increased front end feel. Its 47mm Showa Twin-Chamber fork has the same friction reducing black titanium coating on the lower tubes, but internal damping settings have been tweaked to improve front-to-rear balance (0.44 kg/mm fork and 0.51 kg/mm shock spring rates remain the same). Like before, the fork offers both compression and rebound damping adjustment.
The gas-charged Showa shock absorber also benefits from valving updates, and offers spring preload, high/low-speed compression and rebound damping adjustment. The shock operates through a revised linkage engineered to increase both stability and traction during cornering and reduce the bike’s propensity to hop around when you hit big bumps. Also new is the aluminum swingarm. It utilizes a thinner wall construction as well as decreased internal rib height, further reducing rigidity while contributing to its overall balance.
The black wheels are yet another new component in that both rims are taller and narrower. They’re also said to be stronger and lighter. The rear brake was improved with a different pad material for enhanced feel. The front fender is new with a thicker mounting area said to hold up better to prolonged use, and the seat is also made out of firmer urethane foam which helps maintain its shape.
To find out how the new bike performs we tested it at Castillo Ranch, a private California motocross track hidden in the hills of northern Ventura County. Hop onto its seat and you’ll just how slim of a machine it is. Yet it isn’t so small that it feels awkward for larger riders.
Jump on the kickstart lever and the engine fires immediately whether hot or cold. In fact, the majority of the time one kick was all it took to get us off and running. Out on track the KX-F’s engine spools up fast allowing you to clear obstacles straight out of a corner. But is it quicker than last year’s bike? That’s hard to say. By in large the new bike’s engine felt similar to its predecessor, but that’s fine by us. What we did notice is just how plump its mid-range power is. Motoring up Castillo’s steep inclines really taxes an engine putting a real premium on its ability to pull you forward.
“The motor on this thing is really strong,” said pro-level test rider Matt Armstrong. “I really noticed it on the mid-range. It really kicks as soon as you start revving it and it transitions into a decent top-end. Up top, it revs out really high but it kind
Suspension spring rates remain the same for 2010. Our 160-lb. pro level tester thought that the fork felt soft.
of peters out a bit.”
Although this KX doesn’t utilize fuel-injection, you won’t be able to tell because the jetting is perfect. Crack the throttle and the bike drives forward immediately without hesitation. Even lugging the engine in too high of gear with the throttle pinned does nothing to disrupt its flawless carburetion. If Kawi could keep on cranking out machines that run this perfectly I don’t see the reason why you’d ever need fuel-injection.
One of the inherent traits of a modern 250F is the need to constantly work through the gearbox. We never had any problems with the old bike’s transmission so it wasn’t much of a surprise that this one works great too. We did notice however that there is a considerable gap between second and third gear. While it’s less noticeable on tracks with minimal elevation change, due to Castillo’s steep layout, it becomes pretty apparent. This necessitates a bit of clutch slippage for optimum drive out of some corners. Fortunately, the KX’s clutch is up for the workout. We really appreciated not only how light clutch lever pull is, but how immediately responsive it is – not to mention the amount of outright feel which makes fanning the clutch almost mindless.
Considering how soft and loamy Castillo’s prepped dirt was, it’s hard to discern any differences in the Kawi’s new chassis. In some of the corners the front end had a propensity to push, but again that was due to how soft the dirt was and the fact that the Kawi comes outfitted with an intermediate terrain Bridgestone M403 tire. Yet, the KX250F still impressed with its neutral and stable handling manners.
“The best thing about this bike is its handling,” stated Armstrong. “It turns really well. It’s predicable and never does more or less than what you want. You can get into ruts really easily and the rear end stays planted from entry to exit. Plus it’s stable in the fast stuff.”
While the spring rate inside the fork was soft even for our 160-lb tester, the action both front and rear was phenomenal. Even more impressive was just how well both the ends of the suspension, especially the rear, tracked over square-edged braking bumps that formed on the downhill sections of the track. Not only did the suspension suck up the rough stuff, it virtually eliminated the bike’s rear end from trying to come around during deceleration.
Castillo’s hills put great demands on braking performance and the Kawi’s brakes are some of the best we’ve tested. Although we couldn’t discern an improvement in rear brake feel, we were surprised by just how powerful both brakes are.
The Kawi’s ergonomics package might be one of the most versatile in the class. Not only did the bike fit Armstrong’s 5-foot, 7-inch stature, but it wasn’t that cramped for my five-inch taller frame. As mentioned before the bike is thin, but not so much that it makes squeezing the bike between your legs awkward feeling. We also really like its oversized footpegs and the way the seat is crafted which makes it easy to ply your body forward and backward within the cockpit. Another plus is that its aluminum Renthal handlebar can be moved about an inch forward by just flipping around the bar mounts.
Armstrong demonstrates his whip game, a testament to how effective the 2010 Kawasaki KX250F’s ergonomics package is.
Once again, Kawasaki’s KX250F impressed us with its peppy engine, nimble and composed chassis, as well as its versatile ergonomics package. From accelerating to turning to braking, this bike does it all well, plus it’s an easy motorcycle to ride. In fact, there are only two flaws we can find with the new KX – if you can even call them that. First, while we appreciate every aspect of the bike, there’s nothing that stands out in the “wow” factor. If Kawi could just squeeze a bit more engine power up top, or make it even more flickable this could easily be changed. Finally, dirt bike inflation continues with the MSRP increased by $500 to $6999. So does the new KX have what it takes to go against the redesigned 2010 Honda CRF250F and the rest of the class? We think so, and in a few short months we’ll have the definitive answer.