Spring Creek Motocross
plays host to the Millville Outdoor National each year; a venue capable of thrashing the best MX bikes and riders in the world. Kawasaki used the famous racetrack as the introductory proving grounds for its new 2013 KX250F. MotoUSA made the trip to Minnesota and laid ruts in the sandy loam for two full days of riding on Kawasaki’s latest bid for 250F moto dominance. After watching a detailed presentation on the new model changes, getting the skinny from factory technicians and riding until our bodies ached, it’s clear that green and black machines are going to be fighting for race podiums across the country.
More power – that’s the name of the game with the 250 class. Kawasaki
and the rest of the OEMs might focus on smoothing out their big bikes, but the quarter-liter machines are in a constant search for more ponies. Of course, engineers specifically tailor it into a usable spread, and Kawasaki has made a host of updates for 2013 to ensure the KX250F is covered on both fronts.
Extracting the most performance from an engine requires efficient combustion, and that starts with getting the proper air/fuel mixture delivered into the cylinder. Kawasaki introduced a second injector in its Digital Fuel Injection (DFI) system a year ago. The second injector is located higher (upstream) on the intake tract, and squirts atomized fuel prior to the main injector. Both are four-hole designs but the upstream injector has been repositioned for better fuel delivery. Bigger news, however, is the intake tract itself, which has been reworked to allow for a higher and more direct shot into the combustion chamber. The intake duct is straighter and feeds into a reshaped cylinder head intake. The combination creates a downdraft system that minimizes the bend located right before the intake valve that was present in the 2012 model, thus shooting the good stuff into the cylinder more effectively. The intake valve seats are 4% more dense and the intake cam timing has been retarded by four degrees. Kawi credits these changes with better high-rpm performance and longer durability.
For a more explosive bottom end, Kawasaki boosted the compression ratio to 13.8:1 (vs. 13.5:1). This was accomplished by shortening the cylinder minutely (36.2mm vs. 36.3mm). Engineers also targeted a longer-running motorcycle by changing up the piston skirt in high-pressure areas, and installing a new spark plug cap to help keep out water and mud. The ignition rotor is heavier to help make the power delivery more tractable.
A new exhaust system is part of the engine package that makes
the KX250F a serious ripper. Kawi also provides three different
ignition mapping couplers for quick engine tuning.
A new exhaust system graces the right side of the bike with a MegaBomb-type header which Kawi calls its Acoustic Resonator chamber. The stainless steel head pipe is designed to augment bottom-end power while cutting sound. We noticed that the engineers did a great job of tucking the bulbous pipe in close to the engine. We never felt it while riding and also appreciate the big heat shield. The KX-F also gets a new muffler to match which is 30mm shorter. This brings the weight of the exhaust can closer to the center of the machine. Kawi engineers regain the volume by making it taller and revising the profile. The exhaust outlet is 7mm wider, but KX-F officials claim it still meets the 94 dB requirement. It doesn’t sound any quieter to our ears, but it is slightly less raspy, which most media representative seemed to notice.
“The thing is a rocket ship,” says test rider Frankie Garcia after ripping around Spring Creek MX. “Even better, it doesn’t stand out in one particular area. It has all this bottom-end power and the power just keeps growing all the way until it tops out and hits the rev limiter. It’s insane!”
One of several designs carried over from the 450 is the addition of interchangeable ignition mapping couplers. The bike comes with a trio: stock (green), hard-terrain (black) and soft-terrain (white). The hard terrain mapping smoothes power for more traction and the soft-terrain option makes for a more aggressive hit. We sampled all three on Millville’s varied terrain and could feel a noticeable difference. The stock option is a terrific blend of the two, but both of our testers preferred the black coupler despite a deep ripping during track prep, plenty of water and naturally soft soil around most of the circuit. It has just as much power on tap as the others but is easier to control on corner exits. Our non-pro tester also claims more control while navigating ruts with the smoother, more tractable output.
This is an incredible tool for a racer who faces certain conditions in the morning and then a totally different track in the afternoon. Before the ability to electronically control the fuel system this would have been an expensive and massive chore of swapping exhaust pipes. It’s like Kawi gives the rider three full-system exhausts that you can toss in the toolbox. Changing a coupler takes about 10 seconds. It is located on the throttle side of the steering head and requires no tools. The bike must be shut off completely and restarted, however, or else the altered mapping will not be recognized by the ECU. In addition to the preset couplers, Kawi riders can also use the accessory FI Calibration Kit to create their own custom maps.
A 4mm thinner chassis is also more rigid, which
makes for a sharp turning and stable machine.
Kawasaki adjusted the aluminum perimeter chassis with the intent of increasing overall rigidity, as well as out of necessity. The new intake tract required massaging the frame, but the change riders will notice is a narrower midsection. The main spars are now 4mm narrower, bringing the rider’s knees inward. Having spent plenty of time on the 2012 model, Garcia noticed the difference immediately. Our other tester isn’t as familiar with the ’12 version, but can attest that the chassis feels very slim and nimble.
The steering head and shock tower are stiffer and the upper engine mount is reshaped, though mostly to provide better access to the idle speed adjuster (which is now knurled for easier grip). Lengthening the front portion of the aluminum swingarm by 20mm offers a claimed 4.2% increase in rigidity. Also, the lower triple clamp pinch bolts are located on the side instead of the front which gives the front end less flex.
Kawasaki still employs the Separate Function Fork on its 250F, despite the 450 getting the fancy pneumatic system. That’s fine with us because the front suspension is great. The right fork contains the spring and offers preload adjustability – something we torqued on in conjunction with shock preload for a perfectly tailored ride height. The left leg holds compression and rebound settings. Internally the main piston (rebound) and sub piston (compression) are both larger which stemmed from increasing the lower fork tube from 47mm to 48mm. Damping circuits on the fork and shock have been tweaked for the updated chassis.
One test rider was able to hop on and go virtually all day with only a couple clicks. Our other rider chased the balance setup considerably but was able to finally lock in settings for the final few sessions after toying with nearly every adjustment front and rear. It highlights one of the Kawasaki’s greatest strengths – tunability. Not only are the components good – fork, shock, chassis and tires – but they can be tweaked in so many ways that it’s basically the rider’s fault if they can’t find something pretty darn suitable. Both of our riders were very happy with the end result, noting the updated Showas as an improvement over previous KX-Fs.
“The shock impresses me even more than the fork,” says Garcia. “I never encountered any bucking or swapping. In the corners the shock really stood out when packed hard into a rut where the bike planted extremely well. That, along with the added rigidity, gave a lot of confidence. The front end is really planted also except when hitting sharp-edged braking bumps,” he continues. “That’s when the front got a little knifey and twitchy at times, but it was never a huge issue, especially for stock suspension.”
Revised suspension and upgraded brakes are
capable of handling everything the Millville
track can throw at them.
Millville has a series of steep climbs and drops which put the chassis and suspension to the test, but they also tax the brake systems. A new front master cylinder uses a pushrod-type linkage instead of a knocker-style. The twin-piston caliper also gets new pads that create better friction on the 250mm petal rotor. Both testers had all the braking power and feel they needed, the slower of the two commenting that he never found the limit of the front brake – it just provided more and more grip every lap. New Dunlop dirt bike tires
are mounted front and rear. The MX51FAJ front and MX51J rear are intermediate-terrain treads specifically designed to work with the KX250F’s handling and suspension. The “J” models are only available through Kawi dealers.
Though one finger stays on the lever, the rest of the hands make use of new grips. We can’t feel much of a difference in terms of comfort or durability, but they are each 10mm longer and Kawasaki claims they’ll actually come off when it’s time to replace them. The grips are just the tip of a complete styling redesign and ergonomic adjustments. A flatter seat profile helps the rider move around during cornering. Combined with the thinner chassis, this helps give the bike a very light and manageable feel on the ground or in the air.
“Through rough sections and the Millville whoops, the bike is easy to grip,” says Garcia. “The 4mm change is very easy to identify. It helps with gripping the bike and also made it more comfortable and easier to maneuver.”
Two days on an immaculate Millville track would be great by
any standard, but aboard the 2013 KX250F it was pure MX bliss.
Aside from the KX-F running stronger and handling better, it has the looks to match. All of the main plastic has been changed with an angular front fender, sleek front numberplate, minimal, single-piece shrouds without the holes drilled at the top, side panels with only one seam for less catch points and a matching black rear fender. The suspension adjusters and engine plugs are blue anodized and the clutch and ignition side covers are no longer black. Boots quickly wore off the old finish so now they are a “phantom silver” finish. It’ll go a long ways in keeping the bike looking fresh over time. And speaking of plastic, the Kawasaki also gets new urethane chain sliders that are thicker with higher density.
“The all-new styling is spot on with a modern look,” says Garcia who couldn’t stop gushing over the front end. “When I laid eyes on the new bike, I immediately fell in love with it. The thing just flat out looks badass!”
What else would we like to see? Not much, but how about snagging those adjustable footpegs from the 450 as well? With so many revisions for 2013 the new model feels like a refined, solid package. Not only does Kawasaki offer top-level performance all around, but the KX250F has more adjustability than any other bike in the class. This is a bike that’s capable of working well for a wide variety of racers, and it’s going to be one heck of a platform for Mitch Payton and the Pro Circuit racing team in the coming year.