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2009 Kawasaki KX250F and KX450F Preview

Motocross bikes get an overhaul for 2009

By Staff, Jun. 17, 2008

Kawasaki engineers have decided to give the KX450F and KX250F motocross bikes an overhaul for 2009. Though both bikes received extensive makeovers, the biggest change is that electronic fuel injection is now standard on the 450F.

This is the first major update for both bikes since 2006 when the 450F was introduced and the 250F was outfitted with an aluminum frame.


Kawasaki has basically created an entirely new KX450F for 2009. Included in the many updates is the new fuel-injected engine, chassis, bodywork and durability enhancements. According to Kawasaki, this bike is sleeker, faster and more high-tech than ever.

Key for the KX450F is the upgrade to electronic fuel injection (EFI), which eliminates the need to adjust engine settings to suit track and climate conditions. Kawasaki says the EFI offers stable fuel-metering even in a variety of tough motocross conditions.

Kawasaki basically built a brand new KX450F for 2009.

The new EFI system includes a lightweight ECU, a 43mm throttle body, a newly designed lightweight aluminum in-tank fuel pump and an ultra-fine atomizing injector. Set at a 45° angle for ideal mid-range power, the 12-hole injector sprays 60-micron fuel particles for smooth power delivery and improved engine response at partial throttle.

Designed specifically for motocross, the KX450Fís EFI system can be started within three rotations of the crankshaft, eliminating the need for a battery as it uses only the electricity generated through the kickstarter. To achieve this, Kawasaki engineers had the ECU power-up at the initial movement of the kickstarter. The system delivers electricity in the following order: ECU, fuel pump, and then injector.

A new, larger AC generator rotor handles the electrical needs of the EFI system and increases the engines rotational inertia. A reshaped and lighter crankshaft balances out the bigger ACG rotor, while a wedge-shaped crank web increases the offsetting moment to help achieve a crankshaft balance factor of close to 60 percent - on par with Kawasakiís factory racers. These changes result in reduced engine vibration, smoother power delivery and an improved low rpm throttle response.

The new engine is more compact and lighter, with a 5mm shorter cylinder head that features revised intake and exhaust ports for improved engine performance through the entire rpm range. A new piston with a reshaped top surface raises the engineís compression ratio from 12.0 to 12.5:1 and works in conjunction with a new one-piece titanium exhaust pipe to provide improved low-mid range performance. Also new is a larger-volume silencer body thatís able to meet future noise regulations.

The engine in the KX450F comes standard with electronic fuel injection.
The new aluminum swingarm now pivots from a 3mm higher position on the frame.

Power is said to be delivered with a linear low-rpm throttle response and torque delivery that reduces fatigue.

Kawasaki engineers designed the aluminum frame, suspension components and settings to translate the powerband and responsive throttle into better drive off the corners. Lighter handling and a slimmer chassis with an optimized rigidity balance were also a goal. To achieve this, the cross-sections of the main spars were shrunk, the head pipe is slimmer and a new process was used to form the down-tube, while the reshaped sub-frame is narrower and stronger.

A total of 1.8 pounds of weight savings was achieved thanks to a blend of forged, extruded and cast parts, the revised chassis dimensions, parts reduction and gussets of the new frame. Also, an improved rigidity balance is said to help increase stability and traction.

A new aluminum swingarm is now pivoting from a 3mm higher position on the frame. The swingarm features a more tapered design with a ĎDí profile and new cross bracket. A longer rear suspension stroke and more precise rear suspension tuning were achieved by mounting the arm of the Uni-Trak rear suspension linkage below the swingarm.

The KX450Fís suspension offers many new features for better cornering and sharper handling. The Kayaba Air-Oil-Separate (AOS) fork has a new Diamond-Like Carbon (DLC) coating on the outer surface of the inner fork tubes which offers a claimed 15% reduction in stiction when the fork is exposed to lateral forces that hamper slide action. According to Kawasaki, this results in improved fork response, especially during cornering.

Increasing the rigidity in the reshaped upper triple clamp and decreasing it in the new outer fork tubes optimized the rigidity balance of the front end. Adjusting the suspension settings and reducing the fork offset from 24 to 23mm further enhanced the new lighter handling and increased its front wheel traction. Enlarged, wraparound black fork tube guards provide greater protection for the inner tubes.

The Kayaba rear shock received a new body design and a larger 50mm piston (previously 46mm). Kawasaki says the improved response, damping and bottoming performance equate to a better ride and increased maneuvering precision. It also features a Kashima Coat treatment on the shock internals to help with sealing and friction.
Durability enhancements are not limited to internal components on the new KX450F. The larger, resin skid plate and narrower, longer lasting chain guide both offer better protection without increased weight and are examples of the race-oriented durability improvements that abound on the new KX450F.

Like the KX250F, the KX450F has new bodywork styling, including one-piece dual injected, two-tone green and white plastic shrouds and side number plates. A slimmer new seat design with firmer urethane, a non-slip top surface and smooth sides provides good seated grip and 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. Wider 50mm footpegs offer increased grip and a more comfortable platform.

The 2009 KX450F will be available in Kawasaki Lime Green, with black alumite-coated rims and aggressive graphics for a factory appearance. It will retail for $7,549.


For 2009 the KX250F has been reinvented with a slimmer look and is designed to offer lighter handling, updated ergonomics and a host of changes that Kawasaki says will enhance engine performance and improve durability.

The cylinder head features a new intake port design that is better sealed and holds new stronger titanium valves. New factory-level crankshaft balance and a tapered titanium exhaust pipe claims to help create a smoother power delivery from the 249cc, liquid-cooled, four-stroke engine.

The KX250F has a slimmer look and Kawasaki says itís designed to offer lighter handling and enhanced engine performance.

A revised crank web should also help with balance while reducing engine vibration and improving low rpm throttle response. Cooling capacity in the engine was increased with a new water jacket routing and larger radiators with new louvers. The new louvers are now smaller with a shallower angle to flow more air and now feature four blades instead of three.

To reduce weight engine oil volume was lowered to 1.3L and a KX450F-type crankcase oil filter was added to maintain reliability. Kawasaki says transmission durability was boosted with a bigger interval between the gear shafts, which allows for the use of stronger gears.

Kawasaki reduced the fork off-set by 1mm, enlarged the wraparound tube guards and reshaped and stiffened the upper triple clamp.
The green plastic shrouds and have a longer lasting finish and few graphics to wear off.

Kawasaki switched to a new ratchet-drive shift mechanism and integrated the clutch cable into the crankcase to improve shifting and clutch lever feel. Lever ratios, spring rates and shaft locations were also revised.

The slimmer feel of the 2009 KX250F is partially due to its new aluminum perimeter frame and sub-frame. This new frame uses fewer parts and gussets and is 2.2 lbs lighter than the 2008 model. The main frame spars were reshaped and provide a 6mm narrower overall profile at the riderís knees. A new manufacturing process and down-tube design shed weight and work with relocated engine mounts to improve rigidity balance.

A new aluminum swingarm works in conjunction with the frame revisions and pivots from a higher position on the frame for a claimed improvement in traction. It is a now a lighter, more tapered design with a ĎDí profile and new cross bracket. Mounting the suspension arm of the Uni-Trak rear suspension system below the swingarm resulted in a longer rear suspension stroke and more precise tuning.

A new rear Showa shock with a large 50mm piston diameter, which features a Kashima Coat on the shock internals, has damping characteristics that Kawasaki says offers better response and improved bottoming performance.

Included in the Showa fork upgrades is a Lites-class first: titanium-coated slider tubes. This dark navy blue coating decreases stiction and provides a super-hard surface to help prevent scratches and damage to the tubes. Also, the inner surface of the outer fork tubes has a friction-reducing Kashima Coat treatment.
To optimize rigidity balance Kawasaki reshaped and stiffened the upper triple clamp and reshaped and decreased the rigidity of the outer fork tubes. Other fork enhancements include a 1mm reduction in fork off-set, revised suspension settings and enlarged wraparound tube guards.

A larger, resin skid plate and narrower, longer lasting chain-guide offer greater protection without adding extra weight. The one-piece, dual injected, two-tone black and green plastic shrouds and side number plates have a longer lasting finish and few graphics to wear off.

Beyond updating the look, Kawasaki says the revised bodywork was designed to improve rider comfort and ergonomics. The rider now has a slimmer interface and natural positioning. Ergonomic updates include improved feel from the wider 50mm footpegs, a slimmer seat design with firmer urethane foam, a non-slip surface and smooth sides provides good seated grip and rider mobility.

The KX250F also features premium Renthal aluminum handlebars, black triple clamps, number plates, engine covers, hubs and wheels.

Available in Lime Green, the KX250F will retail for $6,499.

KX450F Specs
Engine Liquid-cooled, four-stroke single with DOHC and four valve cylinder head
Displacement 449cc
Bore x stroke 96.0 x 62.1mm
Compression ratio 12.5:1
Fuel Injection 43mm Keihin Throttle body
Ignition Multi-map digital CDI with throttle position sensor (K-TRIC)
Transmission Five-speed
Rake / trail 27.1 degrees / 4.6 in.
Front suspension / wheel travel 48mm inverted, Kayaba AOS with DLC coated sliders, 22-position compression and 20-position rebound dampening adjustment / 12.4 in.
Rear suspension / wheel travel UNI-TRAK linkage system and Kayaba shock with 22-position low-speed and stepless high-speed compression dampening, 22-position rebound dampening and fully adjustable spring preload / 12.4 in.
Front tire 90/100-21
Rear tire 120/80-19
Front brake Single semi-floating 250mm petal disc with dual piston caliper
Rear brake Single 240mm petal disc with single-piston caliper
Overall length 86.0 in.
Overall width 32.3 in.
Overall height 50.4 in.
Wheelbase 58.3 in.
Ground clearance 13.4 in.
Seat height 38.0 in.
Curb weight 247.2 lbs.
Fuel capacity 1.8 gal.
Color Lime Green
MSRP $7,549

KX250F Specs
Engine Four-stroke single with DOHC and four valves
Displacement 249cc
Bore x stroke 77.0 x 53.6mm
Cooling Liquid
Carburetion Keihin FCR37 and hot start circuit
Compression ratio 13.2:1
Ignition Digital CDI with K-TRIC throttle position sensor
Transmission Five-speed with wet multi-disc manual clutch
Final drive Chain
Frame Aluminum perimeter
Rake / trail 27.7 degrees / 4.8 in.
Front suspension / wheel travel 47mm inverted Showa twin-chamber telescopic fork with 16-way compression and rebound damping / 12.4 in.
Rear suspension / wheel travel UNI-TRAK linkage system and Showa shock with 13-way low-speed and stepless high-speed compression damping, 17-way 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 57.9 in.
Ground clearance 13.4 in.
Seat height 37.6 in.
Curb weight 229.9 lbs.
Fuel capacity 2.1 gal.
Color Lime Green
MSRP $6,499

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