The Kawasaki KX250 is a two a stroke motocross bike that was introduced in 1974. This bike has been ridden to several AMA Motocross wins, including a number of titles. The 2-stroke KX-250 is no longer sold in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 due to lack of equipment and need. For the U.S. Market, the KX450F was introduced in 2006 and utilizes a 4-stroke engine developed using Formula One

Formula One

Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...

 technology.

Liquid Cooled Engine with Kawasaki Integrated Power Valve System

• KIPS system controls exhaust port height for increased power and torque
• Increased flywheel
  Flywheel
  A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
  
   effect helps the rear tire hook up
• The output shaft now has involute splines at the countershaft sprocket for less play, quicker acceleration and increased durability

Keihin Power Jet PWK38S Carburetor with K-TRIC

• New "shorty" design places the mainjet closer to the cylinder for improved throttle response
• Kawasaki Throttle Responsive Ignition Control (K-TRIC) uses a sensor and alter ignition timing according to throttle position and engine speed for better throttle response and more power
• Power jet system uses an electronic solenoid
  Solenoid
  A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
  
   to close a fuel passageway at high rpm to extend the power peak and increase top-end power at over-rev

Airbox and boot

• New airbox
  Airbox
  Motorcyclists and car enthusiasts use the term airbox for what might more properly be described as an air intake chamber. Older engines drew air directly from the surroundings into each individual carburetor...
  
   and stiffer connecting boot improve airflow around the shock to improve top-end power

UNI-TRAK Rear Suspension

• Cast aluminum section is redesigned for less unsprung weight and more rigidity
• Redesigned needle bearings and sleeves reduce unsprung weight and prevent incorrect assembly that can cause them to bind
• The shock now features both low- and high-speed compression damping adjustments
• The shock oil seal head assembly and adjuster cap changed to aluminum and the aluminum shock clevis is now lighter to reduce unsprung weight
• New triple-rate shock spring improves suspension action at full compression

46 mm Upside Down Cartridge Fork

• New aluminum upper fork tubes are smaller in diameter at the upper clamping area (54 mm to 52 mm) for a plusher ride and less weight
• Stronger inner and outer fork tubes have more overlap to improve suspension action, especially on "slap-down" landings
• New rubber bottoming damper and 10 mm longer fork bottoming cone reduce bottoming
• New fork leg lowers with two-bolt axle clamps increase front end rigidity
• Several internal components changed to aluminum

Front and Rear Disc Brakes

• New ceramic
  Ceramic
  A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
  
   coating on backing of rear brake pads insulate them from heat
• Backing plates now thicker to prevent warping under extreme conditions

High Tensile Steel Perimeter Frame

• Upper frame rails lowered slightly to lower fuel tank
  Fuel tank
  A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
  
   and provide flatter seating position
• New aluminum rear sub-frame

Detail Changes

• New graphics and restyled rear fender
  Fender
  Fender Musical Instruments Corporation, commonly referred to as simply Fender, of Scottsdale, Arizona is a manufacturer of stringed instruments and amplifiers, such as solid-body electric guitars, including the Stratocaster and the Telecaster...
  
   and radiator shrouds
• Flatter seat allows freer rider movement
• New handgrips offer better feel
• Rerouted clutch cable for easier pull

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by: naudia vengeace from commerce Texas

Liquid Cooled Engine with Kawasaki Integrated Power Valve System

• Revised porting for increased low-end and mid-range power
• Revised KIPS system controls exhaust port height for increased power and torque
• KIPS governor bearing size is larger for increased durability

Electrofusion cylinder

• Improves heat transfer
  Heat transfer
  Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
  
   for consistent power output
• It is porous so it holds lubrication
  Lubrication
  Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...
  
   well
• It is hard so it resists abrasion and seizure
• Allows closer piston-to-cylinder clearances for more power

Keihin Power Jet PWK38S Carburetor with K-TRIC

• "Shorty" design places the mainjet and slide closer to the cylinder for improved throttle response
  Throttle response
  Throttle response or vehicle responsiveness is a measure of how quickly a vehicle's prime mover, such as an internal combustion engine, can increase its power output in response to a driver's request for acceleration, such as a pedal being pressed...
  
  
• Kawasaki Throttle Responsive Ignition Control (K-TRIC) uses a sensor and alter ignition timing according to throttle position and engine speed for better throttle response and more power
• Revised Power Jet system uses an electronic solenoid to close a fuel passageway at two separate rpm settings to extend the power peak and increase top-end power at over-rev

UNI-TRAK Rear Suspension

• Cast aluminum section is redesigned for less unsprung weight and more rigidity
• The shock now features both low- and high-speed compression damping adjustments
• Aluminum shock components reduce unsprung weight
• Triple-rate shock spring makes shock action even more progressive

46 mm Upside Down Cartridge Fork

• New bladder system helps smooth out jolts and control bottoming
• New .43 kg/mm fork springs
• Polished internal surfaces for smooth action
• New piston assembly on the cartridge is speed sensitive

Front and Rear Disc Brakes

• Redesigned front brake caliper for better feel
• Improved dust seals at the rear brake lever and caliper

High Tensile Steel Perimeter Frame

• Compact and quick handling
• Removable aluminum rear sub-frame for easy access to the rear shock

Detail Changes

• New graphics
• Flat seat allows free rider movement
• New handlebar
  Motorcycle handlebar
  Motorcycle handlebar refers to the steering mechanism for motorcycles. Handlebars often support part of the rider's weight, and provide a mounting place for controls such as brake, throttle, clutch, horn, light switch, and rear view mirrors....
  
   bend for increased rider comfort

2001

First gear ratio changed and flywheel weight changed for better throttle response and acceleration

2002

Higher Compression Ratio, Beefier 48mm forks,new twinspark ignition system, new 2 piece KIPS powervalve, and revalved rear shock.

2005

Even Suspension Layout

Larger Fuel Tank

Larger Radiator

Internal Spark Arrestor

Oppositional Combustion Chamber Layout

Third Gear Ratio Moved Up 0.012 Degrees

Combustion Rate Improved

Leading Fuel Line Made 2 mm Wider for Enhanced Riding Capabilities

Angled Piston Improves Horsepower by 2HP

Riding Position Lowered for Easy Handling

King Hart Racing Chain is Stock

Wobbling at High Speeds is Reduced By Carefully Shaped Air-Intake Ports

An Extra large aftermarket Spark Plug is Stock

Spark Arrestor 1.2 mm Wider

Heat Proof Radiator Tubes Increase Performance

Entire Exhaust System polished on inside for Lower fuel consumption

Radiator Capacity has Increased From 800mls to 1030mls.

Evolved Piston head shape Increases displacement by 4cc

0.25 Litre Engine enhanced by stronger fuel Jets

8 Litre Fuel tank is increased to 8.5 Litres

2006

Renthal aluminum handlebars.

New piston profile and muffler design.

New reed valve stopper to improve low-rpm response

New water-pump impeller

Petal-shaped brake discs

New rear shock w/dual compression adjustability

Kayaba AOS (Air-Oil-Separate) fork w/one-piece TCV sleeve

New graphics and seat cover