More AMA 250 Championships than any Motorcycle in History!
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 KX250F, 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 250 East and West titles, respectively, on their Monster Energy/ Pro Circuit / Kawasaki-backed KXs. Or read 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 shoots 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 stiction, 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 stiction provided by the SFF design, the KX250F’s fork sliders are titanium oxide coated. Lower stiction 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.
2011 Kawasaki KX250F HIGHLIGHTS
Features and Benefits
At a Glance…
New Digital Fuel Injection (DFI) system
New Showa Separate Function Fork (SFF) divides spring and damping functions; springing in the right leg and damping in left provide less stiction, better performance and easier adjustability
Increased engine performance via higher compression and exhaust/intake changes
High-performance piston featuring bridged-box bottom design
Stainless steel exhaust features longer header section and larger-volume muffler
Revised suspension settings front and rear aimed at race-experienced riders
High-Revving, High Performance 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
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
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 stiction and easier adjustability
Fork now allows external spring preload adjustability
Super-hard titanium coating on the outer surface of the inner fork tubes reduces stiction 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
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
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
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 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
2011 Kawasaki KX250F Specifications*
Engine: Four-stroke single with DOHC and four valves
Bore x stroke: 77.0 x 53.6mm
Fuel injection: 43mm Keihin throttle body
Compression ratio: 13.5:1
Ignition: Digital CDI
Transmission: Five-speed with wet multi-disc manual clutch
Final drive: Chain
Frame: 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: 80/100-21
Rear tire: 100/90-19
Front brake: Single semi-floating 250mm petal disc with dual piston caliper
Rear brake: 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: Lime Green
*Specifications are subject to change.
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