2004 Kawasaki KX250
 
With the release of the stunning new KX250F, Kawasaki
proudly enters the high-revving world of 4-stroke
motocrossers. Kawasaki's first 4-stroke motocross
racer was designed for only one purpose: victory in
the 125 class. Since it was developed after its competitors,
the KX250F is loaded with the latest engine and chassis
technology. The result is a very lightweight, easy-to-ride
machine.
Designed to be both more powerful and lighter than
the leading 250 4-stroke, the DOHC, 4-valve powerplant
is loaded with lightweight materials and unconventional
design techniques. The chassis, based on a race-proven
perimeter frame, benefits from a new linkage system
for the Uni-Trak rear suspension that both improves
suspension action and allows a lighter frame construction.
Newly designed bodywork features a slim design and
new seat for improved rider mobility.
The KX250F's key sales features can be summarised
as follows:
- Lightweight - semi-dry sump design, lightweight
engine materials, new-link Uni-Trak that allows
lighter frame construction, special lightweight
rims and tyres
- Easy starting, hot or cold - FCR carburettor with
hot starter, automatic decompression system
- Racer-friendly 4-stroke engine characteristics
- idealised engine braking characteristics care
of a 3D ignition map and idealised crankshaft/rotor
inertia
- Superlative handling and improved rider position
- great handling care of new front fork, high traction
from the new-link Uni-Trak system, improved rider
position from slim bodywork (possible thanks to
new D-section tubing on perimeter frame) and revised
footpeg position
- Thin-wall cylinder head casting results in a very
lightweight and very compact design.
- Lightweight titanium valves (IN: 31 mm; EX: 25
mm) for high-rpm reliability. Oxidising treatment
to valves reduces wear.
- Lightweight exhaust system features a titanium
exhaust pipe "stepped" to a slightly larger diameter
stainless steel pipe. Lightweight silencer has aluminium
body and stainless steel interior. End cap resists
mud plugging.
- Semi-dry-sump design keeps oil away from the crankshaft
to reduce windage loss and contributes to a lower
centre of gravity and reduced weight.
- Oil feed to top end is internal, via the bolt
passageways. This design eliminates the weight and
complexity of external oil lines.
- One-piece water pump/oil filter cover saves weight
and adds to compactness.
- Thin-walled crankcase construction and magnesium
head, generator and outer clutch covers contribute
to the engine's impressively light weight. (Photos
5-7) Chassis
- The new-link Uni-Trak rear suspension system (also
refer to note in the Handling / Riding Position
- Rear Suspension section) allows a lighter frame
construction. Since the link pivots on the swingarm
(unlike in the previous set-up, where it pivoted
on the frame), the suspension loads are no longer
transmitted to the frame directly, eliminating the
need for extra gussets and thicker lower frame tubing
to absorb these loads.
- New front and rear rims feature an extremely lightweight
design.
- The front spokes are stepped both at the nipple
and at the hub for lighter weight.
- Specially designed lightweight rear tyre contributes
to low unsprung weight.
- Automatic centrifugal decompression system fitted
to exhaust cam lifts one exhaust valve to ease starting.
The system's simple construction ensures light weight
and high reliability.
- A hot start system gives quick starts when the
engine is hot. The hot start lever is unitised with
the clutch lever.
- FCR carburettor equipped with hot start circuit.
- An optional cable set-up will allow manual operation
of the decompressor (via a lever on the right handle
grip). This makes it easier to clear a "flooded"
engine.
- 249 cm3 liquid-cooled, 4-stroke Single with DOHC
4-valve head pumps out a wide spread of power.
- Using just the right amount of crankshaft/rotor
inertia contributes to reduced engine braking characteristics.
- AC-CDI ignition uses TPS (Throttle Position Sensor)
and a 3D ignition map to provide ideal ignition
timing for various engine conditions. During acceleration
and deceleration, the system makes adjustments to
the 3D ignition map, resulting in improved acceleration
performance and smooth engine braking.
- Quick-shifting 5-speed transmission uses a ratchet
shift mechanism for a light shift touch. The ratchet
mechanism uses a "phased" shift holder to compensate
for the different shift effort riders tend to use
when up-shifting and down-shifting. * Optional rotors
will be available to allow riders to alter the amount
of engine inertia to suit riding style and track
conditions.
- The KX250F chassis, based on a race-proven perimeter
frame, now has new D-section tubes for the upper
frame rails (43 x 25 mm). The curved outer edges
of the frame rails allow the bodywork to hug the
frame more tightly, for a slimmer design and an
improved riding position.
- Steep castor angle enhances cornering performance.
- The footpegs are located higher and closer together,
allowing more bank angle when turning.
- New Kayaba bladder fork features check valves
on the bladders to control their internal pressure.
The result is improved damping and better fork action
throughout the stroke.
- The most important chassis change from the previous
KX models is the new-link Uni-Trak rear suspension
system. Unlike the previous system in which the
link pivoted on the frame, in the new system the
link pivots on the swingarm. In addition to the
lighter frame construction possible due to the brunt
of suspension loads being absorbed by the swingarm
instead of the frame, a second benefit is that the
shock absorber now moves in an outward arc as it
compresses, rather than moving out and back in.
This smoother, more stable action significantly
improves traction at the rear wheel, particularly
when accelerating.
- Slim exterior design contributes to improved rider
mobility and a better riding position.
- The reshaped seat is flatter and uses a new seat
cover texture that resists slipping.
- Very oversquare bore/stroke ratio of 77.0 x 53.6
mm ensures high reliability at high rpm. Rev limiter
prevents over-revving.
- Composite plated aluminium cylinder is extremely
short to prevent over-cooling of crankcase and subsequent
power loss.
- Forged 2-ring piston is tin plated to reduce wear
and the piston skirts have microscopic grooves to
ensure oil retention and low friction.
- Billet camshafts are carburised for durability
and operate alloy tool steel tappets. Cam profiles
designed for wide powerband and high peak power.
- 37 mm Keihin FCR flat-slide carburettor is equipped
with TPS. Accelerator pump contributes to quick
throttle response. Handle grip and throttle cables
changed to suit the push-pull style carb.
- Silencer's outer cover is screw mounted to allow
easy replacement of silencer packing material.
- Reed valve located between the crankcase and the
transmission case reduces pumping loss for high
output and quick response.
- Oil pump uses a 29 x 4 mm feed rotor and a 29
x 10 mm scavenge rotor.
- The shaft on which the kickstart idler gear spins
also functions as a crankcase breather. Holes in
the shaft and gear create a centrifugal breather
that evacuates air from the transmission cavity.
- Crankshaft big-end roller bearing features a "loose-fit"
cage for high-rpm durability.
- Transmission gears are made of tough DSG-2 (Daido
Super Steel for Gears #2).
- An aluminium skid plate and two plastic side guards
protect the engine.
- Aluminium front and upper engine mounting plates
are used.
- The swingarm is new, and features a new cast bracket
just aft of the shock to suit the new link, new
forged axle holders and light 8 mm chain adjuster
bolts. The new swingarm also features tapered, hydroformed
beams.
- The top clamp uses a lightweight aluminium steering
stem nut and a thin 1 mm stainless steel washer.
Aluminium steering stem is tapered for low weight.
- Compact axle brackets for the front fork use a
new clamping method.
- New front fork guards look great.
- The suspension arm is new and is an aluminium
forging.
- The swingarm's single-piece actuating rod is forged.
The new design is both simple and strong.
- Rear shock features a drain bolt to facilitate
oil changes.
- The upper shock mount is positioned to facilitate
access to the carb.
- New front brake hose routed directly to the front
brake calliper. Thin brake line made of a single
layer of Kevlar contributes to brake feel and reduced
weight.
- Dual-piston front brake calliper uses 27 mm pistons
and is operated by a master cylinder with 11 mm
piston.
- Lightweight rear brake calliper uses 25.4 mm diameter
pistons. Compact calliper ensures adequate clearance
for the muffler when the suspension is fully compressed.
- New brake pedal is forged for high strength and
light weight.
- Stunning all-new bodywork graces the KX250F. It
includes a new tank and seat, longer rear fender,
restyled side covers and new radiator shrouds.
- The right side cover has heat-shielding to deal
with the higher temperatures from the larger silencer.
- Fuel tank capacity is 7.5 litres. Although smaller
than the 2-stroke KX tanks, the more fuel-efficient
4-stroke engine gives the KX250F an increased riding
range.
- "Metafoam" gaskets used to ease maintenance chores.
- Different engine sprockets and carb setting parts
will be available as options.
- Other optional parts include a 20" front wheel,
different constant springs for the front fork and
rear shock, and aluminium and steel rear sprockets
sized +/-2 teeth from standard (48T).
- Lime Green with aggressive new graphics.
- Engine Type - Liquid-cooled, 4-stroke Single
- Displacement - 249 cm3
- Bore and Stroke - 77.0 x 53.6 mm
- Compression ratio - 12.6:1
- Valve system - DOHC, 4 valves
- Fuel system - Carburettor: Keihin FCR37
- Ignition - Digital AC-CDI
- Starting - Primary kick
- Lubrication - Forced lubrication, semi-dry sump
- Transmission - 5-speed, return
- Final drive - Chain
- Primary reduction ratio - 3.350 (67/20)
- Gear ratios: 1st - 2.142 (30/14), 2nd - 1.785
(25/14), 3rd - 1.444 (26/18), 4th - 1.200 (24/20),
5th - 1.052 (20/19)
- Final reduction ratio - 3.692 (48/13)
- Clutch - Wet multi-disc, manual
- Frame Type - Perimeter, high-tensile steel (D-section
tubes for upper frame rails)
- Wheel travel: front - 300 mm, rear - 310 mm
- Tyre: front - 80/100-21 51M, rear - 100/90-19
57M
- Caster (rake) - 26.5°
- Trail - 110 mm
- Steering angle (left/right) - 42° / 42°
- Price: KX250-M2 - £4083.13, KX250-N1 - £4783.13
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