2011 MX Bike
With more AMA Supercross Lites Championships than any motorcycle in history, Kawasaki has massively reworked 2011 KX250F. All told, there are nearly 30 upgrades to the new KX250F, all of which reflect the stunning level of testing and development happening behind the scenes at Kawasaki’s R&D and motocross race teams.
When reworking the new KX250F, engineers started with what’s arguably already the gold standard in 250-class racing – the 2010 KX250F. Just ask Christophe Pourcel and Jake Weimer, who won the 2010 AMA East and West Lites titles, respectively, on their Monster Energy/ Pro Circuit / Kawasaki-backed KXs. Or the long list of enthusiast magazine shootouts that picked the 2010 KX250F as the best motocrosser in its class.
For 2011, the goal was an even faster and more ridable KX250F. On the more powerful side of the equation are loads of engine modifications, all of which have made the latest KX an absolute corner-to-corner screamer. The big news is the addition of Digital Fuel Injection (DFI) that not only helps produce stunning – and more useable – power, but also makes tuning a much easier proposition.
The system, basically identical to the one fitted to the 2011 KX450F, automatically adjusts to suit track and climate conditions, and offers consistent fuel metering and response even when the going gets rough, such as when landing off jumps or slamming through the whoops. The simple and highly efficient DFI system incorporates a compact and lightweight Electronic Control Unit (ECU), a 43mm throttle body, a lightweight aluminum fuel pump and an ultra-fine atomizing injector.
Set at a 45-degree angle for optimum mid-range power, the injector precisely metered fuel directly into the intake tract for smooth power delivery and highly accurate engine response throughout the entire rpm range. The 250F’s injector actually flows more fuel than the 450F’s unit due to the 250F engine’s higher speeds, while airflow through the system is actually higher than through the 2010 model’s carburetor setup.
Designed specifically for motocross, the KX250F’s lightweight DFI system requires no battery; the engine can be started within three rotations of the crankshaft using only the electricity generated through the initial stroke of the kickstarter. What’s more, an optional ECU Setting Tool allows racers to select from several different ECU data maps, or fine tune a custom map that alters fuel injection and ignition timing to suit different tracks and conditions. The tool can also be used as a data logger, recording up to six hours of data, including engine rpm, degree of throttle opening, coolant and air temperatures, ignition timing, fuel adjustments, gear position and system voltage.
You’ll find more significant changes farther downstream, such as higher compression – now 13.5:1 vs. 13.2:1 – via a modified cylinder and changes to the top of the exclusive Bridged-Box Bottom piston. The intake camshaft now produces higher valve lift, while the intake valve spring is stronger to handle the extra load. The crankshaft’s rotational inertia has been slightly modified to better match the new engine’s characteristics, while a slightly longer spark plug design – and a new coil offering a hotter and longer-duration spark – improves combustion performance.
Transmission and final-drive ratios have been altered slightly to match the engine’s newfound response, and a modified shifting mechanism allows you to access those speeds more easily and smoothly. There’s 10% more air-cleaner duct volume for better breathing, and on the exhaust side, a longer head pipe gives the engine a touch more low-end power, while a higher-volume muffler assembly lowers noise to comply with the 94 db AMA Pro Racing limit, while retaining optimum power production up top.
The chassis has been massaged every bit as thoroughly as the engine, with Kawasaki’s new Separate Function Fork (SFF) leading the list of changes. Unlike a conventional fork design, where each fork leg handles both springing and damping, the SFF separates spring and damping functions for improved performance, 25 percent less friction, lower weight and easier adjustability. The right leg accommodates the spring side of the equation, incorporating a larger main spring/rod assembly than traditional forks, plus a small amount of oil for lubrication. Spring preload is now adjustable via a blue-anodized adjuster on the right leg’s cap. The left leg handles damping duty, with only its cartridge damper assembly and fork oil inside the tube.
Rebound and compression damping are adjustable on the fork tube. In addition to the natural reduction in friction provided by the SFF design, the KX250F’s inner fork tubes are titanium nitride coated to reduce friction. Lower friction and better overall fork action are keys to the new fork’s performance, and they are traits you’ll appreciate the first time you charge into a bump-infested corner at speed. Fork offset has also been reduced by a full millimeter for lighter handling and quicker steering response.
Out back, the rear shock incorporates revised damping settings that more closely match the SFF’s performance. The result is even more wheel and chassis control while ripping across a set of whoops or shrieking through that fast, rutted corner leading onto the front straight. Like the KX450F, the new 250F gets a reworked seat with grippier material along the sides for improved rider grip while standing when the action gets hot and heavy.
The rest of the package includes the same top-tier components that have put the KX250F atop the podium for years. The KX250F’s aluminum perimeter frame, with its lightweight blend of forged, extruded and cast parts, has the chassis balance, rigidity and durability experienced riders want and need, and locates the engine, rider and pivot points where they perform best.
Designed with rider ergonomics foremost in mind, the KX250F’s bodywork offers riders a slim interface and a natural positioning that make going fast a simple affair. The sleek bodywork components include one-piece plastic shrouds and side number plates. The upgraded seat provides excellent seated grip and rider mobility, and features firm urethane foam to hold its shape longer. Chassis protection bits include the large, resin skid plate, rear caliper guard and a redesigned chain guide with approximately 2.5 times more durability than the 2010 unit.
The KX’s 249cc, liquid-cooled, four-stroke engine is a veritable powerhouse, and features an electrofusion cylinder treatment on the cylinder bore, a crankshaft balance factor of nearly 60 percent (on par with Pourcel and Weimer’s factory racebikes), for reduced vibration and smoother power delivery, a highly durable – yet slick-shifting – transmission, stronger-than-ever crankcases and a level of reliability that’ll keep you out there and on-track all season long. It’s been rated the best engine in its class by various magazine editors, and you’ll understand their thinking after your very first ride.
The rest of the KX250F package is every bit as impressive as the engine and chassis. Aside from the sort of fit and finish you expect from Kawasaki, there’s also a premium-quality Renthal aluminum handlebar included standard, black alumite-coated aluminum wheels that are both light and strong, a ribless rear hub and butted spokes that further reduce unsprung weight, and factory-style graphics that finish things off nicely and highlight the KX250F’s amazing on-track abilities.
Racers who ride their KX250F at designated events are eligible to receive support from Team Green, Kawasaki’s amateur racing support program. Each year, Team Green provides regional support vehicles and highly trained technicians at more than 100 events throughout the United States, offering technical information and assistance to those who race Kawasaki products.
Kawasaki also offers a comprehensive contingency program for amateur and professional riders who place well at designated events.
Engine: Four-stroke single with DOHC and four valves
Bore x stroke: 77.0 x 53.6mm
Cooling System: Liquid
Fuel injection: 43mm Keihin throttle body
Compression ratio: 13.5: 1
Ignition: Digital DC-CDI
Transmission: Five-speed with wet multi-disc manual clutch
Final drive: Chain
Frame Type: Aluminum perimeter
Rake/Trail: 28.2 degrees / 4.7 in.
Front suspension / wheel travel: 47mm inverted Showa SFF telescopic fork with spring preload adjustability and 22 position compression and 20 position rebound damping adjustability/ 12.4 in.
Rear suspension / wheel travel: Uni-Trak® linkage system and Showa shock with 19 position low-speed and stepless high-speed compression damping, 22 position rebound damping and fully adjustable spring preload / 12.2 in.
Front Tire Size: 80/100-21
Rear Tire Size: 100/90-19
Front brakes: Single semi-floating 250mm petal disc with dual piston caliper
Rear Brakes: Single 240mm petal disc with single-piston caliper
Overall length: 85.4 in.
Overall width: 32.3 in.
Overall height: 50.0 in.
Wheelbase: 58.1 in.
Ground Clearance: 13.0 in.
Seat height: 37.2 in.
Curb weight: 232.7 lbs.
Fuel capacity: 1.9 gal.
Color Choices: Lime Green