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Kawasaki Releases Details and Photos of 2007 KX four-strokes

2007 Kawasaki KX250F

Kawasaki released details of it’s 2007 MX line-up today, including a host of changes to its KX 250F and KX450F four-strokes. With the factory’s effort focused entirely on the four-stroke MXers, the two-stroke KXs continue for next year with basically no changes.

Here is Kawasaki’s press release regarding the KX™250F.

Kawasaki’s all-new four-stroke KX™250F rose to the top to become one of last years best motocross bikes. For 2007, Kawasaki improves the championship winning KX250F with a host of engine and chassis modifications designed to extend its performance advantage.

Refinements to Kawasaki’s highly acclaimed KX250F make it an even more potent track weapon. The newest KX250F keeps the outstanding top-end power from last year’s bike, but adds a stronger pull from the bottom of its rev range.

The upgraded engine is complimented by a strengthened 5-speed transmission and a revised chassis featuring increased longitudinal rigidity for lighter, quicker steering.

The new KX250F will be available in Kawasaki lime green with new color matched wheel hubs and aggressive new graphics.

KX250F key features include:

  • 249cc water-cooled overhead-cam engine with titanium valves
  • New polished intake ports. This extremely-smooth surface improves intake flow at every rpm
  • New longer, straighter airbox funnel contributes to increased low-rpm response
  • New intake valves have thicker skirts and are held by longer guides for increased durability
  • Ultra-light thin-stem valves are further strengthened by a special treatment on their skirts
  • New, looser-fitting piston ring with reduced tensile strength lowers friction
  • Revised piston crown contributes to improved power at high-rpm
  • Revised carb tuning and ignition timing to suit the engine’s modifications
  • New 20mm taller right-side radiator offers increased cooling capacity
  • An all-new 5-speed transmission with thicker gears offers improved shifting and increased durability
  • New fork sub-springs, revised front and rear suspension valves and a new rear main spring provide a more progressive response for a better ride and increased bottoming resistance
  • New shock spring and revised valving for improved suspension action
  • A new rear shock damping adjustment needle allows more precise tuning of the sear suspension
  • New sub springs and revised valves for the Showa twin-chamber fork contribute to lighter, quicker handling and superior suspension action
  • New works-style aluminum skid plate for added protection
  • New rear rim with a rib-less hub and butted spokes is lighter and stronger than last year’s wheel
  • New “sprocket-style” chain roller helps smooth engine braking by reducing drive lash
  • New shift drum with modifications to the ratchet mechanism and a new ball Bearing shift lever improve shift feel
  • New stiffer clutch springs (up roughly 20%) gives more direct feel at the lever

Here is Kawasaki’s press release regarding the 2007 KX™450F.

Kawasaki enhances the dynamic excellence of its world SX championship winning KX™450F motocross machine with a new 5-speed gearbox plus a host of engine and chassis refinements aimed at increasing its domination over the competition.

The 2007 KX450F offers all the dirt-shredding power from last year’s bike, with enhanced bottom end and midrange thrust for even quicker acceleration from the starting gate and stronger drive out of corners. This revised engine tuning is coupled with a new 5-speed transmission to allow greater flexibility in gear selection and increase the rider’s options on the track.

Kawasaki also lavished attention upon the KX450F’s frame and suspension. With a change to the frame’s downtube and new fork internals, the ’07 KX 450F boasts improved rear wheel traction and enhanced flickability, to maximize acceleration and offer easier line selection when passing the competition.

The new KX450F will be available in Kawasaki lime green with color matched wheel hubs and aggressive new graphics.

KX450F key features include:

  • 449cc water-cooled overhead-cam engine with titanium valves
  • Revised engine tuning provides stronger low-through mid-rpm performance, with the same championship winning top-end rush
  • New 5-speed transmission offers better choices for dealing with technical track sections
  • New ball bearing shifter mechanism for smoother and more precise shifting
  • Thinner frame downtube reduces torsional rigidity for quicker turning and lighter steering
  • Larger 41mm titanium exhaust header for increased power
  • Larger front fork damper cartridges with revised valving for a more progressive and plush action
  • Revised fork seals and inner liners for reduced stiction
  • Revised rear suspension linkage, shock mounting and shock valving maximizes traction for better acceleration
  • Lighter and stronger rear hub for increased durability and less unsprung weight
  • New sprocket style chain roller reduces drive lash
2007 Kawasaki KX450F