The KX250 motorcycle represents the epitome of Kawasaki's two-stroke motocross development, and it arrives for 2005 with major revisions to the engine and chassis, resulting in more power and better handling to help keep KX250 racers at the head of the pack.

Kawasaki engineers began by creating an all-new Kawasaki Integrated Power Valve System (KIPS®) for the liquid-cooled 249cc two-stroke engine. Previously, the main and sub valves operated simultaneously, causing a power surge after a slight gap in the 6,000 to 7,000 rpm range. By having the valves operate independently, the sub valves begin to open only after the main valve is fully open. Power comes on more smoothly, resulting in a more linear powerband, improved traction and overall more tractable power characteristics. Plus, the cylinder's forward mounting angle has been reduced from 10 degrees to five degrees, which, allows for the use of a longer exhaust port, further enhancing power across the rev range.

The engine's coolant passageways within the cylinder are also redesigned for improved cooling, particularly around the exhaust port, to prevent heat-induced power fade during long motos.

The most significant modification to the lightweight steel perimeter frame is a decrease in steering rake from 27 degrees to 26 degrees, which quickens steering response for superb cornering performance. The frame's stiffness balance has also been improved, and a new lower swingarm bracket improves ground clearance.

While the design of the aluminum swingarm remains unchanged, the wall thickness of the main spars is increased for enhanced stability and handling.

Changes to the front suspension include new twin-chamber Kayaba forks, which help to keep oil and air separate for stable damping performance during long motos, and low-friction fork seals contribute to smoother action.

In addition, the new UNI-TRAK® rear suspension system features redesigned linkage ratios to suit the new frame and swingarm.

The revised frame is narrower at the footpegs, giving the bike a slimmer feel, and higher footpegs complement the new riding position while increasing ground clearance. The rear brake pedal is also mounted 15mm higher for increased ground clearance, and to suit the new riding position.

Other ergonomic changes include a revised handlebar bend, which contributes to improved rider mobility, and a new seat that is flatter and raised 10mm higher for improved rider mobility. The seat cover also uses a high-grip top and smooth sides for good grip when sitting and high mobility when standing on the pegs, while more durable urethane foam improves comfort and wear.

Features and Benefits

Engine/Transmission

• Head gasket changed from metal gasket to O-rings for improved sealing and more accurate deck height
• New intake design features a single port with modified length and angle for improved intake efficiency
• Scavenging port exit angle is changed for improved scavenging efficiency, and the crankcase mating area around the scavenge ports has been increased. Third scavenging port also modified for improved flow
• New reed valve angle, air guide and reed block are changed for improved throttle response
• Intake air duct is reshaped to suite revised intake manifold
• New expansion chamber dimensions and improved construction (changed from four-piece to a three-piece) contributes to improved engine performance
• Redesigned piston uses new rings and new piston sealing grooves to prevent ring snagging; stronger pin boss improves durability
• Clutch release shaft and lever modified, and release mechanism moved behind generator cover
• Shift performance improved by using involute splines on the fifth gear and on the output shaft. A needle bearing added to the shift shaft improves shift feel
• New water pump uses new pump gear ratios and a new impellor for increased coolant circulation, plus a new water jacket around the exhaust port eliminates the need for an external coolant hose
• Sprocket cover, governor cover, inner/outer clutch covers, and water pump cover changed to suit new crankcases
• Generator cover changed from plastic to magnesium for improved appearance and increased functionality
• Revised carburetor settings contribute to improved throttle response, and a new carb holder allows straighter incoming airflow
• Radiator core length increased (from 220 to 240 mm) for improved cooling performance
• Upgraded ignition system features increased condenser capacity and a generator with a built-in regulator for light weight. Stator shape changed, and new wiring harness used. Ignition timing changed to suit new power characteristics
• New, shorter spark plug eases maintenance and weighs less
• New, lightweight ignition coil is more compact
• Ignition coil primary terminals feature waterproof couplers for increased reliability
• Low-friction throttle barrel also reduces throttle operating friction

Rider Controls

• Stainless throttle cable wire with a greater number of thinner strands delivers superb, low-friction throttle operation
• Clutch cable outer liner changed from polyethylene to Teflon for reduced friction
• Clutch adjuster added to clutch lever perch
• New front brake lever has better feel

Chassis/Suspension

• Steering rake reduced to 26 degrees to quicken steering response
• Footpegs are wider and offer better grip; shorter transverse length means greater cornering clearance
• Wider handlebar mounts (increased from 90 to 98 mm) help prevent handlebar bending
• New lightweight DID front rims with lightweight spokes and nipples reduce unsprung weight
• New cross-section for rear rims also designed for light weight
• Light fork and shock mounting bolts and a new rear brake master cylinder with a unitized reservoir and shorter yoke (17.5 mm shorter than '04 KX250) contribute to light weight
• Fork mounting bolt locations changed on the top triple clamp for easier maintenance and stronger mounting
• New front brake pad material offers better feel and performance
• Chain guide roller now uses two bearings for greater durability
• Rear subframe has larger forged upper mounting brackets for improved durability
• Fuel tank filler outlet is increased form 37 to 46mm for easier fueling
• Carburetor tuning parts
• Ignition rotors with different inertial weights
• Larger 14T front sprocket
• Spark plugs of varying heat ranges
• 20-inch front wheel
• Solid brake discs
• Aluminum and steel rear sprockets
• Different fork and shock springs
• Steel spoke nipples
• Front and rear wheel assemblies