Kawasaki KX250F & KX450F Receive Major Upgrades For 2011

Tuesday, May 25th, 2010

The KX250F & KX450F base package provides an excellent platform for race-experienced riders to win races in the top classes.

Design of the highly rigid aluminium frame, suspension components and settings focused on ensuring control is maintained during high-speed riding – especially in straight lines –
to enable experienced racers to ride full out. And to deliver holeshot-winning performance – a key factor that can mean the difference between running up front and winning, or
getting stuck mid-pack – chassis geometry and the high-revving 4-stroke engine’s wide powerband were designed to maximise rear wheel traction. The combination is a proven
race-winner, with multiple AMA Supercross Lites and Motocross Lites championships to its credit.

To ensure the Lime Green racers continue to run at the front, Kawasaki engineers made a number of engine and chassis changes to further increase the KX250F’s & KX450F’s winning potential.

High-Revving Fuel-Injected Engine

Tuned to best suit race-experienced riders, the 249 cm3 liquid-cooled, 4-stroke Single’s wide powerband focuses on high-rpm performance and extends way into the over-rev.

Already featuring race-inspired tuning and parts like the high-performance piston with bridged-box bottom (a mass-production first when introduced on the 2010 KX250F), the 2011 engine receives fuel injection and a number of changes for even more power, stronger low-mid range torque (most noticeable when riding through the whoops, landing jumps and coming out of tight turns, it allows riders to shift less often, reducing fatigue and enabling quicker lap times), more accurate shifting and a quieter exhaust note.

Factory-racer engine tuning High-performance piston, featuring the same design used on our factory racers, contributes to improved performance at all rpm, A short skirt, reinforced external ribs and the industry’s only mass-production use of a bridged-box bottom, featuring fully flush internal bracing, result in a lighter, stronger piston.

• A new piston crown, revised to suit chamfering of the squish area, offers increased high-rpm and over-rev performance.
• Intake camshaft with revised sprocket/shaft arrangement retards intake valve timing 1o, to suit the new fuel-injected engine.
• A new spark plug protrudes 1.4 mm deeper into the combustion chamber, improving combustion efficiency.
• Intake ducting has about 10% greater volume, resulting in improved response (especially in the ultra-low rpm range).

The revised intake ducting and new deep-protrusion spark plug not only offset the drop in low-mid torque that comes from a change to fuel injection, performance is actually improved in this range.

• Revised final reduction ratio offers improved engine feel. The shorter gearing (13/48T >> 13/50T) further accentuates the increased low-end torque.
• Cylinder height reduced (36.5 mm >> 36.3 mm) to suit the new piston and higher compression ratio: now 13.5:1 (previously 13.2:1).
• Exhaust pipe is longer (480 mm >> 510 mm) to suit new engine characteristics.

Battery-less fuel injection system

Designed specifically for motocrossers, the fuel injection system incorporates a small lightweight ECU and operates without a battery to further eliminate unnecessary weight.

And of course, fuel injection eliminates the need to adjust engine settings to suit track and climate conditions.

Ensuring quick starting without a battery was a prime directive when developing this fuel injection system. Using only electricity generated by the kick starter, the engine can be started with only three rotations of the crankshaft. The system delivers electricity in the following order:

1) ECU, 2) fuel pump, 3) injector. With a warm engine, starting can be accomplished in a single kick.

The compact, lightweight ECU, located just in front of the steering head (behind the number plate), was designed specifically for motocross use. To help cope with the shocks and vibrations of motocross riding, the fuel pump relay is built in to the ECU.

A 43 mm throttle body makes use of a progressive throttle link to deliver airflow in much the same way as would a FCR carburettor. Using two linked shafts, the throttle body opens more quickly after the 3/8 open position, delivering sharp response and excellent power feeling.

Lightweight throttle body is approximately half the weight of a FCR carburettor – a weight savings of about 600 g.

To ensure the high-rpm engine’s demand for a high flow of gas in a short period is met, the KX250F’s injector features larger holes than that used on the KX450F. A fine atomising injector with 4 holes disperses spray particles with a droplet size of 120 μm. Fuel flow is about 20% greater than on the KX450F.

The newly designed fuel pump, located in the fuel tank, is a lightweight aluminium construction. (Fuel tank capacity is now 7.2 litres.)

To ensure a stable fuel supply during vigorous motocross riding the fuel pump features a rubber fuel filter cover that wraps around the inlet port and acts as a fuel trap. A fuel return hose from the pressure regulator ensures there is always fuel in the fuel trap.

Factory KX FI Calibration Kit (option)

The KX FI Calibration Kit is the same kit used by Kawasaki’s works teams in Europe and the U.S. The kit enables expert riders to adjust engine characteristics (by rewriting actual
data maps) to suit their preference, record riding data, and analyse their riding data to further fine-tune their settings.

The KX FI Calibration Kit contains KX Racing software, an ECU controller, mounting brackets and damper, harness and USB cable. In addition to the kit, a PC and 12 V battery are all
that is required.

While the kit is designed to satisfy racers and expert riders, it is simple and hassle-free to use:

• the ECU controller mounts behind the number plate for easy access - accessing the ECU is accomplished simply by connecting to a PC via the ECU controller using a USB cable (no additional switches are necessary) - setting adjustments can be prepared in advance on a PC, or done when connected to the ECU - the kit’s user-interface is simple to understand and easy to use

The KX FI Calibration Kit contains seven preset settings that can be quickly and easily used to adjust the ECU to suit track conditions. The provided settings are shown below.

1. Richer fuel setting: fuelling 5% richer than stock
2. Leaner fuel setting: fuelling 5% leaner than stock
3. Advanced ignition setting: ignition advanced 3˚ from stock
4. Retarded ignition setting: ignition retarded 3˚ from stock
5. Hard riding surface setting: ignition retarded, fuelling richer
6. Soft riding surface setting: ignition advanced, fuelling leaner
7. Beginner setting: engine power suppressed: ignition retarded, fuelling richer

For more advanced setting optimisation, the ECU maps for volume of fuel injected (via the FI adjustment window) and ignition timing (via the IG adjustment window) can be adjusted for given throttle position and rpm.

High-Speed Chassis With Factory-Style Components And Tuning

The KX250F’s slim aluminium perimeter frame is a lightweight construction composed of forged, extruded and cast parts. Chassis balance and settings were all set to suit race-experienced riders. The centre of gravity and key dimensions (swingarm pivot, output sprocket and rear axle locations) were chosen so that the rear tyre would drive the bike forward (instead of causing it to squat). For ’11 the high-speed chassis benefits from a new Separated Function front Fork (SFF) with greatly reduced friction that offers increased riding comfort and improved suspension performance. In addition to enhanced handling offered by the SFF’s improved left/right balance, increased chassis flex and revised frame rigidity balance offer lighter handling and increased turning performance. The highly acclaimed high-speed stability of its predecessor remains unchanged.

Lighter-handling chassis

While the frame remains essentially the same as that of the 10MY model, revised rigidity balance results in a frame with moderate lateral flex. Frame’s front and side hangers (engine mounting brackets), previously aluminium, are now formed from steel, and are thinner (front: t6.0 mm >> t4.5 mm; side: t8.0 mm >> t4.5 mm).

The resultant increased lateral chassis flex enables lighter turning. The revised rigidity balance offers a number of benefits:

• increased rear wheel traction
• more planted feel from the front wheel
• enhanced cornering accuracy makes it easier for riders to follow the line they want

Reduced fork offset (23.5 mm >> 22.5 mm) also contributes to the lighter handling, enhanced cornering accuracy and more planted feel of the front wheel. Additionally, it also gives the bike a more compact feel.

Superior rear-wheel traction

The New Uni-Trak rear suspension system mounts the suspension arm below the swingarm, allowing a longer rear suspension stroke. The longer stroke in turn allows more precise
rear suspension tuning.