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In June Wheels24 published the first images and details of the fierce Kawasaki KX 250F motocross racer. Now we have finally have received the full lowdown.
Not content with the success of 250cc machine (which has been called the Gold Standard in AMA 250 class motocross racing in the past) Kawasaki’s technical department made more than 30 significant changes to the bike.
New digital fuel injection ensures extra grunt
The single biggest change to the motocross racer is the shift from a carburettor to a lightweight battery-less digital fuel injection system for 2011.
This and the other mechanical changes to the engine were made to produce more grunt, particularly low-down and midrange power, allowing riders to get away with fewer gear changes between corners and jumps, and thus combat race fatigue.
One of the developmental priorities was to ensure that the bike would start quickly, despite not having a battery. The system works much like that of the KX 450F, with the engine requiring just three rotations of the crankshaft to deliver current generated by the kickstarter action to first the ECU, then the fuel pump, and finally the injector of a cold engine. With a warm engine starting can be accomplished with a single kick.
Because of the high-revving nature of the KX 250F, the bike’s fuel injection system uses larger injector holes than those of the KX 450F, allowing it to flow 20% more fuel than the bigger bike. A lightweight aluminium fuel pump is safely housed out of harm’s way inside the fuel tank.
Calibrated for maximum efficiency
Apart from the more precise and refined power delivery offered by the new fuel injection system, the rider or race mechanic can now use Kawasaki’s optional KX FI Calibration Kit to tune the motor for maximum effect on race day.
The kit contains KX Racing software, an ECU controller, mounting brackets and damper, a harness and a USB cable. After hooking up a PC and a 12-volt battery the serious racer can adjust engine characteristics by rewriting actual data maps to suit his preference, and record and analyse data to assist in further tuning the system.
The KX FI Calibration Kit also contains seven preset modes that quickly and easily change fuel mixtures and ignition settings for a range of scenarios - there’s even a beginner setting to tame the motorcycle’s manners for novices still getting used to dirt riding.
New piston delivers higher compression and increased redline
The engine of the new Kawasaki KX 250F has also been fettled to give it a performance advantage in 2011. A new lighter piston with a special crown designed to improve the squish area gives a higher compression ratio, higher rpm and improved over-rev performance, while a new spark plug protrudes 1.4mm deeper into the combustion chamber to improve combustion efficiency.
The intake camshaft has been altered to make better use of the new fuel injection system, and intake ducting giving 10% more volume results in improved throttle response, particularly at ultra low revs. Cylinder height has been reduced from 36.5mm to 36.3mm to suit the new piston and elevate compression ratio to 13.5:1, (up from 13.2:1) and the exhaust has also been redesigned.
Trick fork assembly ensures smoother damping and less friction
A big change to the suspension is the Separate Function Front Fork (SFF) that offers significantly reduced friction, a smooth action and firm damping performance. Instead of the two front forks each replicating the duties of the other, the SFF system allows each to specialise.
The left fork tube contains the damping assembly, while the right houses the front end’s single heavy-duty spring. The benefits of this are that the friction between the springs and the fork inner tubes is reduced by about 25%, while the damper piston in the right fork can be bigger, making for smoother action and firm damping performance.
There’s also now space in the right fork for a preload adjuster, which greatly simplifies the task of adjusting preload and front ride height. Where most of the adjustment was previously effected by fiddling with the rear shock, ride height and preload can now be swiftly and effectively set at both the front and rear ends of the motorcycle.
Some of the other enhancements in the long list of changes are improved petal brake discs front and rear, a lighter handling chassis with revised rigidity and lateral flex characteristics, a 1mm reduced fork offset for improved front-end feel, new plastics for a slim profile, a slip-retardant seat, wider footpegs, a new throttle grip, a robust lightweight synthetic material skid plate, a new front chain guide to extend chain life and a longer gear ratchet lever with a lighter return spring to reduce chances of a missed shift without changing feedback from the lever.
There wasn’t much that needed fixing on the 2010 Kawasaki KX 250F but the engineers did themselves proud in turning it into an even better machine for 2011. Whether you’re a weekend recreational rider or a national championship contender there’s no doubt that the newest KX 250F deserves a second look.
The 2011 Kawasaki KX 250F retails at R66 995 inclusive of VAT.
Kawasaki KX 250F technical specs
Engine: Four-stroke single with DOHC and four valves
Displacement: 249cc
Bore x stroke: 77.0 x 53.6mm
Cooling: Liquid
Fuel injection: 43mm Keihin EFI
Compression ratio: 13.5:1
Ignition: Digital CDI
Transmission: Five-speed with wet multi-disc manual clutch
Final drive: Chain
Frame: Aluminium perimeter
Rake / trail: 28.2 degrees / 120,2 mm
Front suspension: 47mm inverted Showa SFF USD telescopic fork
Rear suspension: New Uni-Trak linkage system and Showa shock
Front brake: Single semi-floating 250mm petal disc with dual piston caliper
Rear brake: Single 240mm petal disc with single-piston caliper
Overall length: 2170 mm
Overall width: 820 mm
Overall height: 1270 mm.
Wheelbase: 1475 mm
Ground clearance: 330 mm
Seat height: 945 mm .
Curb weight: 105,7 kg
Fuel capacity: 7.2 litres
Not content with the success of 250cc machine (which has been called the Gold Standard in AMA 250 class motocross racing in the past) Kawasaki’s technical department made more than 30 significant changes to the bike.
New digital fuel injection ensures extra grunt
The single biggest change to the motocross racer is the shift from a carburettor to a lightweight battery-less digital fuel injection system for 2011.
This and the other mechanical changes to the engine were made to produce more grunt, particularly low-down and midrange power, allowing riders to get away with fewer gear changes between corners and jumps, and thus combat race fatigue.
One of the developmental priorities was to ensure that the bike would start quickly, despite not having a battery. The system works much like that of the KX 450F, with the engine requiring just three rotations of the crankshaft to deliver current generated by the kickstarter action to first the ECU, then the fuel pump, and finally the injector of a cold engine. With a warm engine starting can be accomplished with a single kick.
Because of the high-revving nature of the KX 250F, the bike’s fuel injection system uses larger injector holes than those of the KX 450F, allowing it to flow 20% more fuel than the bigger bike. A lightweight aluminium fuel pump is safely housed out of harm’s way inside the fuel tank.
Calibrated for maximum efficiency
Apart from the more precise and refined power delivery offered by the new fuel injection system, the rider or race mechanic can now use Kawasaki’s optional KX FI Calibration Kit to tune the motor for maximum effect on race day.
The kit contains KX Racing software, an ECU controller, mounting brackets and damper, a harness and a USB cable. After hooking up a PC and a 12-volt battery the serious racer can adjust engine characteristics by rewriting actual data maps to suit his preference, and record and analyse data to assist in further tuning the system.
The KX FI Calibration Kit also contains seven preset modes that quickly and easily change fuel mixtures and ignition settings for a range of scenarios - there’s even a beginner setting to tame the motorcycle’s manners for novices still getting used to dirt riding.
New piston delivers higher compression and increased redline
The engine of the new Kawasaki KX 250F has also been fettled to give it a performance advantage in 2011. A new lighter piston with a special crown designed to improve the squish area gives a higher compression ratio, higher rpm and improved over-rev performance, while a new spark plug protrudes 1.4mm deeper into the combustion chamber to improve combustion efficiency.
The intake camshaft has been altered to make better use of the new fuel injection system, and intake ducting giving 10% more volume results in improved throttle response, particularly at ultra low revs. Cylinder height has been reduced from 36.5mm to 36.3mm to suit the new piston and elevate compression ratio to 13.5:1, (up from 13.2:1) and the exhaust has also been redesigned.
Trick fork assembly ensures smoother damping and less friction
A big change to the suspension is the Separate Function Front Fork (SFF) that offers significantly reduced friction, a smooth action and firm damping performance. Instead of the two front forks each replicating the duties of the other, the SFF system allows each to specialise.
The left fork tube contains the damping assembly, while the right houses the front end’s single heavy-duty spring. The benefits of this are that the friction between the springs and the fork inner tubes is reduced by about 25%, while the damper piston in the right fork can be bigger, making for smoother action and firm damping performance.
There’s also now space in the right fork for a preload adjuster, which greatly simplifies the task of adjusting preload and front ride height. Where most of the adjustment was previously effected by fiddling with the rear shock, ride height and preload can now be swiftly and effectively set at both the front and rear ends of the motorcycle.
Some of the other enhancements in the long list of changes are improved petal brake discs front and rear, a lighter handling chassis with revised rigidity and lateral flex characteristics, a 1mm reduced fork offset for improved front-end feel, new plastics for a slim profile, a slip-retardant seat, wider footpegs, a new throttle grip, a robust lightweight synthetic material skid plate, a new front chain guide to extend chain life and a longer gear ratchet lever with a lighter return spring to reduce chances of a missed shift without changing feedback from the lever.
There wasn’t much that needed fixing on the 2010 Kawasaki KX 250F but the engineers did themselves proud in turning it into an even better machine for 2011. Whether you’re a weekend recreational rider or a national championship contender there’s no doubt that the newest KX 250F deserves a second look.
The 2011 Kawasaki KX 250F retails at R66 995 inclusive of VAT.
Kawasaki KX 250F technical specs
Engine: Four-stroke single with DOHC and four valves
Displacement: 249cc
Bore x stroke: 77.0 x 53.6mm
Cooling: Liquid
Fuel injection: 43mm Keihin EFI
Compression ratio: 13.5:1
Ignition: Digital CDI
Transmission: Five-speed with wet multi-disc manual clutch
Final drive: Chain
Frame: Aluminium perimeter
Rake / trail: 28.2 degrees / 120,2 mm
Front suspension: 47mm inverted Showa SFF USD telescopic fork
Rear suspension: New Uni-Trak linkage system and Showa shock
Front brake: Single semi-floating 250mm petal disc with dual piston caliper
Rear brake: Single 240mm petal disc with single-piston caliper
Overall length: 2170 mm
Overall width: 820 mm
Overall height: 1270 mm.
Wheelbase: 1475 mm
Ground clearance: 330 mm
Seat height: 945 mm .
Curb weight: 105,7 kg
Fuel capacity: 7.2 litres
