Kawasaki says:
It’s an old refrain: The factory guys get all the good stuff. Their bikes are faster, lighter and just plain tricker than the motocrossers you can buy off the showroom floor. There’s some truth there. But that’s changing. The gap between production and factory-prepped motocrossers has never been narrower. And with the introduction of Kawasaki’s massively reworked 2011 KX™250F, that gap just shrank a little more.
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 race teams. And Kawasaki does this for one reason: To put you on the fiercest, most capable motocrosser in the industry.
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.
Features:
Higher Performing, High-revving Engine
- 249cc, liquid-cooled, four-stroke, four-valve, single-cylinder DOHC engine delivers hard-hitting power across the rpm range
- Modified intake valve timing and cam profile for increased valve lift improves high-rpm power production
- Intake valve spring tension increased to control more radical cam timing
- Digital Fuel Injection (DFI) system allows consistent fuel delivery, quick starts and easy adjustability
- Engine tuned to achieve the widest possible torque band to maximize traction through a greater percentage of the rev range
- Race-experienced riders able to harness high-rpm performance that extends way into the over-rev
- Sprocket-style chain drive roller helps reduce the effect of driveline lash and engine braking for smoother and faster corner entries
- Crank web design features a balance factor on par with the factory racers for reduced engine vibration, smoother power delivery and increased performance in the mid-high rpm range
Digital Fuel Injection (DFI) System
- Same basic system that’s fitted to the KX450F
- 43mm throttle body assembly with 20 percent higher-flow injector than the KX450F’s injector
- Intake airflow is higher than on carburetor-equipped 2010 model
- Progressive throttle link; opens more quickly after 3/8 open position
- Simple and efficient system: No battery, fuses or relays
- Improves engine response across entire rpm range
- Offers easy engine starting
- Prevents engine hesitation after landing from jumps and other high-impact situations
- Optional Calibration Kit allows easy tunability
- Optional FI Indicator Light allows the DFI system to communicate diagnostic information
Bridged Box-bottom Piston
- Light and strong piston shares same design as the factory racers, with a revised crown for higher compression. Also features fully flush internal bracing
- Short piston pin reduces reciprocating weight
Lightweight and Efficient Top End
- Lightweight, highly rigid, titanium 31mm intake and 25mm exhaust valves reduce reciprocating weight and offer high-rpm reliability
- Ultra-light valves have extremely thin valve stems on par with those found in supersport machines; intake valves feature thick heads for increased strength
- Intake ports designed for peak performance at all rpm, especially in the high-rpm range
- Special coating applied to intake port cores during casting gives the intake ports extremely smooth surfaces and optimum intake efficiency across the rev range
- Silicon-coated head gasket provides excellent sealing
Enhanced Durability and Reliability
- Electrofusion treatment on cylinder bore improves surface oil retention, while the molybdenum coating on the cylinder bore surface helps resist scorching, further contributing to durability
- Wide big-end bearing features a thick copper plate on its cage and a long crank pin for increased reliability
- Oil pump rotors offer a high degree of reliability and durability; a large feed pump rotor maximizes oil flow, while a smaller scavenge-pump rotor reduces mechanical losses
New Stainless Steel Exhaust System
- Stainless steel construction offers extra durability
- Longer header pipe section for improved low and mid-range response
- Higher-volume muffler assembly quiets emissions to 94 dB noise regulations while retaining power production
- Joint between pipe and muffler offers excellent sealing, while a rubber damper collar on the rear silencer mount equals serious durability
Efficient Cooling System
- Thick and wide radiators are strong and offer excellent resistance to mud buildup while providing superb cooling performance
- Cylinder head water jacket routes coolant to the front of the cylinder head for even cooling
Transmission and Shifting Reliability
- Third and fourth input gears have large dogs to help prevent wear
- Revised ratchet and lever angle for more positive shifting
- Revised internal ratios for second and fourth gear better match new engine power delivery
- New 50-tooth rear sprocket helps capitalize on the engine’s torque delivery
- Strong, beefy crankcases feature additional material around the engine mounts to help increase long-term durability
- Clutch cable holder is integrated with the crankcase for accurate feel at the clutch lever
- Scavenge oil filter screen can be accessed without splitting the crankcases, facilitating easier maintenance
Quick-turning Chassis
- Utilizes a low-rigidity steering stem for lighter handling
- The KX250F’s slim and lightweight aluminum perimeter frame is composed of forged, extruded and cast parts
- Center of gravity and key dimensions such as swingarm pivot, output sprocket and rear axle locations designed to increase forward drive with minimal rear-end squat
- Upper engine mounts on head cover sides increase overall rigidity
Race-oriented Suspension
- Revised race-oriented suspension damping settings optimize front/rear balance
- New Separate Function Fork (SFF) separates springing and damping functions for less weight, better performance, less friction and easier adjustability
- Fork now allows external spring preload adjustability
- Super-hard titanium coating on the outer surface of the inner fork tubes reduces friction and improves suspension action. The increased surface hardness also helps prevent scratches and tube damage
- Friction-reducing Kashima Coat treatment on the inside of the outer fork tubes contributes to smoother suspension action
- Wrap-around fork tube guards provide greater protection for the inner tubes
- Revised shock damping settings offer increased absorption performance and greater stability on corner entry thanks to reduced rear-end kicking
- Features Kashima Coat on the inside of the shock reservoir for reduced friction and smoother suspension action
- Rear shock features dual compression adjustability, allowing high-speed and low-speed damping to be tuned separately
Superior Rear-wheel Traction
- Swingarm features optimum internal bracing and flex characteristics for improved cornering performance
- Alloy swingarm uses a cast front section, tapered hydroformed spars and forged chain adjusters
- Uni-Trak® rear suspension system mounts the suspension arm below the swingarm, allowing more rear suspension stroke and precise tuning
- Linkage ratios for the Uni-Trak rear suspension match rear shock damping settings to achieve maximum rear wheel traction
Rider Interface
- Bodywork components offer the rider a slim interface, making it easy for racers to feel comfortable and go fast
- Formed using a double-injection molding process, the two-tone shrouds offer a slim design
- Side number plates also two-toned and contribute to the slim package
- Right side panel has an added passageway to help cool the silencer
- Frame is wider at the ankles to offer better grip and narrows near the bend below the seat to allow a slim riding position
- Slim seat features firm urethane, which keeps its original shape longer
- Seat has a slip-resistant top and side surface for good grip when seated and while standing
- 50mm wide (front-to-rear) footpegs offer superb grip and feel at the pegs
- Clutch cable boot features a large quick adjuster, making it easy for riders to adjust play in the clutch cable while on the fly
- Throttle grip has a one-piece collar that provides additional stability during throttle operation
- Lightweight short-length grips feature a pattern designed to provide excellent grip
Factory-style Components
- Black alumite-coated rims, just like the factory racers
- Lightweight rims offer maximum strength and weight savings
- Thick and rigid front fender
- Rear brake pad material offers powerful braking performance
- Front and rear petal brake discs help reduce unsprung weight, and the wave shape helps clean the brake pads for more efficient braking performance
- Rear caliper guard protects caliper from damage
- Ribless rear hub and butted spokes further reduce unsprung weight
- Renthal aluminum handlebar is standard equipment
- Factory-style graphics complement the KX250F’s highly tuned performance
Additional Features
- Large front brake lever boot offers increased protection against debris
- Newly designed and more durable chain guide utilizes a thicker wear pad for longer life
- Large resin skid plate offers great protection with minimum weight
Optional Accessories
- Optional DFI Calibration Kit allows custom tuning
- Optional FI Indicator Light allows the DFI system to communicate diagnostic information
- Engine parts include magneto rotors with different inertias and a 12-tooth output sprocket
- Optional chassis parts include handlebar holder for a 1 1/8-inch handlebar, 46
- to 50-tooth aluminum and steel rear sprockets, solid petal brake rotors, different fork and shock springs and manual decompression lever and cable
Specs:
Engine: Four-stroke single with DOHC and four valves
Displacement: 249cc
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
Photos
Kawasaki says:
In the 450cc motocross game, the only thing that matters to serious racers is top-tier performance and running up front. And for 2011, the best tool for the job is once again a lime green one – Kawasaki’s reworked and revised KX™450F. In this arena you can’t stand still technically, which is why Kawasaki engineers scrutinized every system and component of the race-winning 2010 model and came up with a host of tweaks that’ll have red, blue, orange and yellow wondering what hit ’em.
The latest open-class KX starts with the primary pieces that allowed the 2010 KX to win more Supercross events than any other bike last year – a brutally fast 449cc DOHC four-stroke single packing a broad spread of power housed in a lightweight-yet-strong aluminum frame connected to a suspension designed to offer compliance, high-speed stability and whoop-sucking performance all moto long. It was an ideal platform on which to win the majority of races in 2010, and that trend promises to continue with the revised, even faster 2011 model.
Last year, the KX450F featured a number of engine refinements, including the first ever production use of a bridged-box bottom piston (more high-end power and better over-rev characteristics), revised cam timing for better mid- and top-end performance and a reinforced cylinder sleeve and crankcase for improved durability.
This year there’s even more. The bridged-box bottom piston shape, for instance, has been modified to meld with the upgraded, higher-volume muffler, which is quieter than last year’s unit. The ECU has been tweaked to provide a hotter and longer-duration spark for improved low-rpm response. The shift mechanism incorporates a larger internal roller and stronger shift-spring tension for more positive shifting. Finally, the fuel-injection system’s Calibration Kit software has been updated, while the controller harness and connector have been modified for easier use.
Changes in the chassis department are equally impressive, and show the results of our race team’s effect on development. First up are revisions to the engine mount brackets that optimize chassis flex and improve handling. Next, the engineers revised the damping settings for the massive fork tubes for even better performance. For that factory-bike touch there are also blue-anodized compression damping adjuster caps in place of last year’s silver ones. Damping settings on the rear shock have also been revised, and it, too, gets a blue-anodized compression adjuster. The seat features a new side-surface texturing for increased rider grip while aboard, and the drive chain guide has been thoroughly beefed up for increased durability; testing shows it to be nearly three times more durable than the unit fitted to the 2010 machine.
The race-ready engine is compact and light, with a short 100mm cylinder head and a 12.5:1 compression ratio. A wedge-shaped crank web offsets 60 percent of the crankshaft’s reciprocating weight, producing an effective “counterweight” effect. This is on par with Kawasaki’s factory racers and helps reduce engine vibration, smooths power delivery and enhances low-rpm throttle response. A stainless steel exhaust pipe connects to the revised silencer, which uses long-fiber packing material to maximize service intervals. A rubber damping collar in the rear silencer mount provides a boost to long-term durability. The KX450F’s Digital Fuel Injection (DFI®) automatically adjusts to suit track and climate conditions, and offers stable fuel metering even when landing from jumps in tough motocross conditions. The DFI system includes a compact and lightweight ECU, a 43mm throttle body, a lightweight aluminum fuel pump and an ultra-fine atomizing injector. Set at a 45-degree angle for ideal mid-range power, the 10-hole injector sprays precise, 60-micron fuel particles for smooth power delivery and accurate engine response throughout the rpm range.
Designed specifically for motocross, the KX450F’s lightweight DFI system doesn’t require a battery; the engine can be started within three rotations of the crankshaft using only the electricity generated through the initial stroke of the kickstarter.
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, engine boost, coolant and air temperatures, ignition timing, fuel adjustments, gear position and system voltage.
The engine’s phenomenal power is delivered through a clutch that features an ultra-light operating plate with superb oil drainage and beefy friction plates. The entire assembly is designed to provide exceptional clutch feel and durability. The drive chain features thin inner links and a slight weight savings relative to typical designs to help boost acceleration. The revised suspension damping settings provide lighter handling, improved suspension action, increased comfort and greater cushioning when landing from jumps.
The 2011 KX450F’s D-shaped aluminum swingarm features a cross section with narrow ribs and thin walls. It pivots high in the aluminum frame to maximize rear wheel traction. Mounting the arm of the Uni-Trak® rear suspension linkage below the swingarm provides a long rear suspension stroke and facilitates precise shock tuning.
Complementing the responsive chassis is a Kayaba Air-Oil-Separate (AOS) fork that offers precise cornering and sharp handling. The fork features a Diamond-Like Carbon (DLC) coating on the outer surface of the inner fork tubes to minimize stiction when the fork is exposed to lateral forces that would otherwise restrict slide action. The result is smooth and precise response, especially during cornering. Overall suspension action is extremely smooth due to a friction-reducing Kashima Coat treatment on the inside surfaces of the outer fork tubes and the rear shock reservoir. Wrap-around fork guards provide excellent protection for the sliders.
The 2011 KX450F’s Kayaba rear shock’s revised damping settings contribute to improved wheel control and impact performance when landing from jumps. It features a large 50mm piston and a Kashima Coat treatment on the shock internals to help maintain a plush feel throughout the toughest motos. Easily accessible dual compression adjusters allow high- and low-speed damping to be tuned separately, giving mechanics and riders the ability to easily fine tune the suspension for difficult track conditions.
A slim seat design with firm urethane foam and a non-slip top and side surface provides even more seated and standing grip while retaining excellent rider mobility. The frame echoes the slim profile at the top, but widens at the lower end by the ankles to provide the rider with better feel and control. Completing the rider interface are wide 50mm footpegs that offer tenacious grip and a comfortable platform.
The 2011 KX450F is available in Kawasaki Lime Green, with black alumite-coated rims and aggressive graphics for a factory appearance.
Racers who ride their KX450F 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.
Source: Kawasaki USA
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