Kawasaki Reveals Radically New 2011 KX250F

The new SFF allows the rider to adjust not only compression and rebound, but spring preload as well.

Yeah, yeah, it’s fuel injected. But there is a much bigger “wow” factor to Kawasaki’s new 2011 KX250F – the revolutionary new Separate Function Fork (SFF). Separate function as in spring on one side and damping on the other. The asymmetrical design of the fork puts the spring in the right tube, utilizing a larger main spring/rod assembly, and a small amount of oil for lubrication. The left tube houses the single cartridge damping assembly and fork oil.

With this separate function also comes separate fine tuning options. The left fork has the traditional compression and rebound adjustability while the right tube allows the rider to set spring preload.

Kawasaki says that the SFF improves performance, lowers weight and produces 25 percent less stiction than a traditional fork (and we’re pretty sure it won’t cause the KX to constantly veer to one direction like an RV on a windy day). Also new on the latest fork are titanium oxide-coated fork sliders and a one-millimeter reduction in the offset.

The 2011 Kawasaki KX250F Click to enlarge photo.

Back to the motor department, the KX250F carries a refined 249cc DOHC motor with a battery-less Digital Fuel Injection (DFI) system which is essentially identical to that of the 2011 KX450F. The 250 is fed by a 43mm throttle body and actually has a 20 percent higher-flow injector than the 450 (which also has a 43mm throttle body). The 250 receives a new bridged-box-bottom piston (which was debuted on last year’s KX450F) and the cylinder is modified to boost compression from 13.2 to 13.5:1. A longer headpipe delivers better bottom end, and the new muffler drops noise levels to 94 dbA to comply with the new AMA Pro Racing standard.

Kawasaki’s 450 also gets a shot in the arm regarding power output – though we can’t say that the big KX has ever left us wanting more. But we’re glad to hear that the “massively powerful engine” features a piston shape that works in synch with a higher-volume muffler which promises to keep the noise down.

The KX450F receives revised suspension settings – though not the SFF fork of the KX250F. Improved shifting performance, refined ECU settings and a new seat round out the notable changes to the premier class Kawi.

The following is information released by Kawasaki...

 

2011 Kawasaki KX™250F

Features and Benefits

Cutaway of the KX250F's all-new Separate Function Fork. Click to enlarge photo.

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

Click to enlarge photo.

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 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

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

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2011 Kawasaki KX™450F

2011 Kawasaki KX450F Click to enlarge photo.

Features and Benefits

At a glance…
• Massively powerful engine
• Revised suspension settings
• Improved shifting performance
• Revised seat
• Refined ECU settings
• Easier fuel injection calibration system access
• Still easy to start!

Engine Overview
• 449cc liquid-cooled, DOHC, four-stroke single
• Bridged-Box Bottom piston design offers optimal engine performance
• Reinforced crankcase is strong and durable
• A forward lean angle of 3 degrees puts the engine in the ideal position for maximum traction
• Tuned for a broad powerband with the torque curve set just under the wheelspin threshold
• High-acceleration cams help the engine rev quickly
• Maintenance-free automatic cam chain adjuster
• Large airbox flap helps prevent mud and water from entering

Bridged-Box Bottom Piston
• Same design as used on our factory racers; offers improved performance at all rpm
• Lighter and more durable than traditional piston designs
• Short piston skirt features low-friction coating for reduced mechanical losses
• Reinforced external ribs for strength and durability
• Revised profile with fully flush internal bracing results in a lighter, stronger piston
• Short piston pin offers increased strength

Cylinder Head
• Compact head is only 100mm tall
• 36mm titanium intake and 31mm exhaust valves with aluminum spring retainers minimize reciprocating weight and cylinder height to help ensure reliable valve control at high rpm
• Double valve springs allow a short cylinder head height and help ensure stable valve operation
• Camshafts, lobes and tappet surfaces feature a soft-nitride treatment for long wear and high-rpm reliability

Crankshaft
• Crankshaft with high inertial mass helps maximize rear wheel traction
• Wedge-shaped crank web provides enough offsetting moment for a 60 percent balance factor – and is similar to the crank balance in Kawasaki’s factory race engines, resulting in reduced engine vibration, smoother power delivery and increased performance, with a noticeably snappier response at low rpm
• Crankshaft and connecting rod feature a special carburizing and quenching treatment to maximize rigidity

Digital Fuel Injection
• Self-adjusts to atmospheric changes for easier starting, sharper throttle response and optimized power and stability when jumping/landing
• It is not necessary to re-tune, or change any jets to suit climatic conditions like on a carbureted model
• Ultra-fine atomizing injector with 10 holes sprays particles with a droplet size of 60 microns for smooth power delivery and engine response throughout the throttle range
• 43mm throttle body uses a progressive throttle linkage to deliver airflow in much the same way as an FCR carburetor
• Using two linked shafts, the throttle body opens more quickly after reaching the 3/8 open position
• Lightweight throttle body is approximately half the weight of a FCR carburetor, saving over one pound in weight
• Fast-idle knob on the throttle body allows riders to increase engine speed when starting a cold engine
• Fuel injector set at 45 degrees, the optimum angle for mid-range power

High-performance ECU
• New ECU programming and revised settings offer improved response at low-mid rpm
• No battery needed; the engine can be started with only three rotations of the crankshaft using the electricity generated by a single kick of the starter
• The system delivers electricity to FI system in sequence: first the ECU, then the fuel pump, and finally the injector for quick, easy starting
• Starting can be accomplished in a single kick
• The compact, lightweight ECU, located on the front of the steering head behind the number plate, was designed specifically for motocross use. The fuel pump relay is integrated with the ECU to help cope with the shocks and vibrations of motocross riding

Optional User ECU Setting Tool
• Allows racers to reprogram the ECU’s data maps for volume of fuel injected and ignition timing to alter engine characteristics to suit rider preferences
• 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 temp, air temp, ignition timing, fuel adjustments, gear position and system voltage

Easy Starting
• Strong output from the large ACG rotor provides enough electrical power for the battery-less FI system to enable true one-kick starting without using a battery
• Equipped with an automatic compression release (ACR) system for quick and easy starting. The dual-weight centrifugal decompression system is fitted to the exhaust cam
• Compression release features 1.0mm of valve lift, to minimize the required kicking power

Lightweight Aluminum Fuel Pump
• Located in the fuel tank but at a new angle to help prevent damage in extremely rough riding conditions
• Features a rubber fuel filter cover that wraps around the inlet port and acts as a fuel trap to help ensure a stable fuel supply during vigorous motocross riding
• 1.9-gallon fuel tank is formed using a rotational molding process

Efficient Cooling
• High-capacity Denso radiators feature tightly packed cores and a fin design that delivers superior cooling efficiency
• Radiators don’t need reinforcing brackets, which results in lower overall weight
• Shrouds feature a slim design that melds with the radiators’ design
• Radiator louvers feature four small blades set at a shallow angle for minimum overlap and maximum air flow

Strong and Durable Clutch
• Clutch assembly provides a direct feel and superb control
• Excellent oil drainage contributes to more direct feel
• Friction plates with substantial friction material contribute to a more direct feel
• Large operating plate pusher reduces the clearance between the pusher and the input shaft hole, improving clutch operation

Close-Ratio 5-Speed Transmission
• 5-speed transmission and low-rpm engine response combination offers riders more gear options for traversing rough sections or getting into the rhythm of a course easily so they can focus more on racing
• Thinner inner-link chain is light and strong
• Sprocket-style chain drive roller reduces the effect of driveline lash, helping smooth engine braking and facilitating additional corner entry control

Exhaust
• Short, one-piece stainless steel exhaust pipe contributes to optimum mid-high rpm performance
• Optimized exhaust routing contributes to improved ergonomics
• High-volume silencer helps meet noise regulations – currently 94 dB
• Right side panel has special passageway to help cool the silencer

Powerful Disc Brakes
• Rear brake pad material offers strong braking performance
• Powerful twin-piston hydraulic front caliper
• Lightweight semi-floating 250mm petal-type front brake rotor
• Single piston hydraulic rear caliper squeezes lightweight 240mm petal-type rotor

Light, Slim Chassis
• Revised engine mount brackets optimize frame rigidity for better handling
• Lightweight steering stem shaft contributes to light, nimble handling
• Main frame spars are 68mm tall and 24mm wide to provide an ideal balance between stiffness and compliance
• Weight-saving features include a slim head pipe, narrow cross-section and a downtube formed with a swaging (squeezing and hammering) process
• Swingarm pivot is located high in the frame to maximize rear wheel traction

Aluminum Swingarm
• Cross-section design contributes to light handling
• Tapered “D” shape swingarm provides ideal rigidity for excellent stability, and is lighter than a comparable box-section unit
• Alloy swingarm features a cast front section, tapered hydroformed spars and forged chain adjusters
• Uni-Trak® rear suspension linkage ratio maximizes rear traction performance
• Suspension arm is mounted below the swingarm to allow a longer rear suspension stroke and more precise tuning

Front Fork
• Race-oriented suspension settings offer maximum overall performance
• Revised damping settings offer improved action and increased comfort during the initial phase of the suspension stroke
• Kayaba Air-Oil-Separate (AOS) fork keeps oil and air in separate chambers for stable damping performance during long motos. Low-friction fork seals contribute to smooth action
• Diamond-Like Carbon (DLC) coating on the outer surface of the inner fork tubes offers minimum stiction when the fork is exposed to lateral forces that would usually hamper slide action. The result is improved fork response, especially during cornering
• Friction-reducing Kashima Coat on the inside of the fork’s outer tubes contributes to smooth suspension action (especially at the initial part of the stroke) and a superb ride feel
• Wrap-around fork tube guards offer effective protection for the sliders

Rear Shock
• New damping settings contribute to increased stability and improved impact performance when landing from jumps
• Rear suspension settings and linkage ratios derived from extensive rider testing
• Kayaba rear shock features a large 50mm piston
• Rear shock features dual compression adjustability, allowing high-speed and low-speed damping to be tuned separately
• Also features Kashima Coat treatment on the cylinder for reduced friction and smoother suspension action
• Easy adjuster access for track-side suspension tuning

Rider Interface and Styling
• Dual injected two-tone, one-piece plastic shrouds and side number plates
• Optimized exhaust routing contributes to improved ergonomics
• Right side panel has special passageway to help cool the silencer
• Black plastic covers, triple clamps, engine covers, and black alumite-coated rims – just like Kawasaki’s factory teams
• Wide 50mm footpegs provide excellent feel and a comfortable platform
• Frame is wider at the ankles to offer optimum grip, narrows below the seat to allow a slim riding position
• Slim seat design uses firmer urethane foam that keeps its original shape longer for the best possible ergonomics and feel
• Seat has a slip-resistant top surface for good grip when seated and a new material along the sides for extra grip when standing

Additional Features
• Skid plate made of resin material offers great protection without excess weight
• Clutch cable boot features a large quick adjuster, making it easy for riders to adjust play in the clutch cable on the fly
• Increased front axle collar diameter transmits more feedback from the contact patch to the rider
• Ribless rear hub and butted spokes offer light weight and excellent durability
• Rear caliper guard helps protect the caliper from damage