MX Bike Video
For 2011, the goal was an even faster and more ridable Kawasaki KX250F. On the more powerful side of the equation are loads of engine modifications, all of which have made the latest KX an absolute corner-to-corner screamer.
The big news is the addition of Digital Fuel Injection (DFI) that not only helps produce stunning – and more useable – power, but also makes tuning a much easier proposition.
The system, basically identical to the one fitted to the 2011 KX450F, automatically adjusts to suit track and climate conditions, and offers consistent fuel metering and response even when the going gets rough, such as when landing off jumps or slamming through the whoops.
The simple and highly efficient DFI system incorporates a compact and lightweight Electronic Control Unit (ECU), a 43mm throttle body, a lightweight aluminum fuel pump and an ultra-fine atomizing injector.
Set at a 45-degree angle for optimum mid-range power, the injector precisely metered fuel directly into the intake tract for smooth power delivery and highly accurate engine response throughout the entire rpm range.
The 250F’s injector actually flows more fuel than the 450F’s unit due to the 250F engine’s higher speeds, while airflow through the system is actually higher than through the 2010 model’s carburetor setup.
| 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 friction,
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 |
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| Higher Performing, High-revving 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 |
|
| 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 friction and easier
adjustability • Fork now
allows external spring preload adjustability • Super-hard
titanium coating on the outer surface of the inner fork tubes reduces
friction 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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