Kawasaki KX250F - Special Edition eMag

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Special Edition Full Test

Specifications

Now with: Fuel Injection & SFF Forks

2011 Kawasaki

Kawasaki has added some cutting-edge technology to make the KX250F even better for 2011‌

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Test by Todd Reed Photos By Nigel Paterson

Perfectune

Kawasaki’s KX250F has been one of the best motocross machines available in recent years – and for 2011 the Green Machine has made it even better.

TWO years after injecting its KX450F Kawasaki has finally done the same to its KX250F. Even though the previous KX250F was ‘only’ fitted with a carburettor it was still winning races and championships the world over. Now with fuel injection and totally new front forks, the 2011 model is set to do the same in the future.

Engine

Kawasaki’s 250cc four stroke engine is an absolute ripper. It is known around the world for its strong predictable power and excellent reliability. For 2011 the green team has stayed with what it knows and has made some minimal but effective changes to its latest 250cc thumper. The bridged-box piston has been re-designed and now features a a new crown design. Along with a new shorter cylinder this will raise the compression ratio to 13.5:1 and make the bike feel more punchy and lively without compromising any reliability. The intake cam timing has been modified along with a higher valve lift, all to better suit the new Digital Fuel Injection system. Once all this was complete the exhaust got an overhaul to meet the latest noise requirements. The rest of the engine features on the KX250F are similar to years gone by, big strong radiators do a great job

of cooling the little green thumper along with an excellent clutch and gearbox which will last forever and perform like the factory equipment.

The final gearing has been shortened in 2011 to 13/50.

Electronic Fuel Injection EFI is definitely one of the hottest topics being tossed around the pits at any MX track in Oz, so when Kawasaki made public that it was releasing fuel injection on the 2011 KX250F the stories and myths erupted of what was being expected by the weekend warriors around the country.

For those who are stuck in the past and don’t do technology, this means the carburettor is gone, your collection of jets and needles are no longer needed and all the carby knowledge that you have built up over the past 100 years can go on the shelf, right next to all that two-stroke stuff.

Digital Fuel Injection or ‘DFI’ if you like, is the technical name given to the new Fuel Injection System which has been specifically designed for Kawasaki’s latest Lites creation.

The Keihin system utilises a 43mm throttle body which is not too dissimilar to the body

found on its older brother the KX450F. One of the key features of the Kawasaki DFI system lies within two linked shafts that control the throttle speed.

Once the rider twists the throttle beyond the 3/8 mark the linked shafts work together to increase the opening speed of the throttle.

This allows for sharper throttle response at higher RPM. The injector featured is also a totally new design from the Kawasaki engineers, it is claimed to increase fuel flow by at least 20 per cent over its previous injector design which is featured on the current model KX450F. A nice touch which is available as an option on the KX250F is the KX FI calibration kit. It is an aftermarket plug in kit that enables the rider or mechanic to log onto the DFI system and make modifications to both fuel www.cycletorque.com.au – 5

and ignition settings. The pack comes pre-set with seven optimised fuel and ignition curves which were developed by the Kawasaki engineers. You can also play and fiddle as you like and create your own fuel and ignition settings using the software provided with the kit.

Suspension

In 2011 the Kawasaki engineers have introduced their revolutionary new Showa Separate Function front Fork system (SFF). The new front suspension system is vastly different from any other 250cc four stroke on today’s market. In years gone by both damping and springs were housed together in the same fork. Not anymore, the left hand fork now houses the damping assembly only and the right hand fork takes control of the spring assembly.

This allows for dramatically reduced friction and a much smoother, more predictable ride. Kawasaki’s new fork design also saves significant weight over the previous system, the SFF set-up sheds the kilos by dropping parts which were previously needed twice. Now there is only one fork spring and damping system instead of two. It was also evident that after watching the Kawasaki technicians, the new Separate Function front Fork system is quite easy to adjust and simple to work on. All the normal clickers that we are used to seeing were still there, however there is now an added clicker adjuster on the top right hand fork to increase or decrease the amount of preload the rider/ mechanic would like on the front fork spring. The UniTrack rear shock and linkage setup remains relatively unchanged from 2010. The Showa shock gets revised damping settings to match the new fork setup and keep the green machine under control.

The rest

The moment you hop on the KX250F you feel comfortable and ready to go. Headlining the cockpit are Renthal 7/8” handlebars, we know they aren’t the oversize ’bars some riders expect but it’s pretty tough to bend a set of 7/8” Renthals. The bend is very comfortable and is actually the same handlebar that comes on one of its close competitors, the CRF250R. The standard footpegs get the job done,

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however with the latest trend going towards platform widestyle footpegs it would be nice to see the KX with a big chunky set of ’pegs. Kawasaki has opted to fit out the new KX with Bridgestone tyres; the 403 front and 404 rear have an excellent reputation, they offer excellent grip in most conditions and don’t wear out too fast. The black wheels also make the KX look pretty trick.

The overall look of the bike hasn’t changed from 2010 with the exception of the Bold New Graphics. Considering the KX has a slick and modern new look, and that most 250F riders are going to kit their bikes out with new graphics and stickers anyway, having a similar look to last year can’t be a bad thing.

On the track

So what does all of the above mean on the track? It means the 2011 bike is considerably improved over the 2010 bike.

When you first kick over the little green Kawie you notice the DFI has cleaned up the annoying splattering that you get under warm up on a carburettered four stroke. DFI also loses the fuel on/off switch as the need is gone, however there is still a choke knob for those cold early morning race-day starts. Once the KX is all warmed up and you take to the track the feel at the throttle is much more predictable and gone is any evidence of a miss or flutter.

We took it easy to begin with and got used to the set-up of the new fork and shock as well as the DFI. The Showa SFF suspension does an excellent job of soaking up the bumps and feels nice and plush at the top of the stroke. Once we began to tackle some of the bigger jumps the SFF forks and Uni-Track shock held up very well as we took on the big hits with confidence. The motor was very punchy and lively for a small bore thumper. The little green machine pulls very strong off the bottom and doesn’t let off through the mid and top end. Once you spin a few laps on the KX250F it’s quite easy to see why this is a class leading engine.

Verdict

There is no doubt the 2011 KX250F is going to be a winner. Straight off the showroom floor this thing is in race-shape. With over 30 improvements to the 2011 model, Kawasaki has proved it isn’t resting and has taken its new machine to the next level. n

SFF Forks…

Kawasaki claims its Separate Function front Fork (SFF) offers significantly reduced friction, providing smooth fork action and firm damping performance. It’s the first time we’ve see a system like this on a motocrosser: the Italians especially have produced suspension with the compression damping in one leg and the rebound in the other, but Kawasaki’s gone a step further in dropping the spring from the left tube and putting all the damping responsibilities on just one side.

This cutaway shows the preload adjuster at the top of the left fork leg.

Changing spring rate means just switching one spring.

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SFF Forks‌

Kawasaki claims another benefit of the SFF is reduced friction, resulting in better comfort and that means less fatigue.

Another benefit is an improved balance in the front end, as the weight of the disc and caliper offset the weight of the spring in the right fork tube.

All the external adjustments are simpler and quicker, because there are less of them. There’s a preload adjuster on the top of the right fork leg (which simplifies the task of setting fork preload or front ride height) Compression damping is handled by a single adjuster at the top of the left fork leg.

Rebound damping is controlled via a screw at the bottom of the left fork leg. Compression damping is handled by a single adjuster at the top of the left fork leg.

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More power with Fuel Injection…

IN TYPICAL Kawasaki fashion, the Green Machine isn’t the first to the party: the Kawasaki isn’t the first 250 four-stroke MX bike with fuel injection, but it could be the best.

Aimed at experienced motocross racers, the 2009 model was basically all-new, the 2010 updated for more power and now the 2011 features improved bottom end and mid range, as well as better response, thanks to the adoption of fuel injection. But while having a good bottom-end and mid-range can be useful and handy (especially in the whoops, landing off jumps and in tight turns), winning motocross races is about top-end, and here the KX250F won’t disappoint, with the fuel injection improving the bike’s performance in the over-rev, too.

The KX250F’s fuel injection system doesn’t require a battery, the kickstarter providing enough power to start the bike even when cold. It uses a small, designed-for-motocross lightweight ECU, located behind the front number plate and incorporating the fuel pump relay. One of the big advantages of fuel injection is it removes the need to adjust for altitude and climactic conditions, the electronics doing that on the fly.

Because the 250 revs much harder than the 450, the KX250F’s injector holes are actually 20 per cent larger than the bigger bike’s. It also features a progressive throttle link – two linked shafts means the throttle opens quicker after 3/8 throttle to deliver better response and feel.

The 43mm throttle body is about half the weight of a carburettor. There’s an aluminium fuel pump in the 7.2-litre fuel tank which has a fuel trap to ensure it always has fuel to deliver to the EFI despite the rigour of motocross.

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The throttle body is lighter than a carburettor and features twin shafts (see below) for better feel and progressive fuel delivery: fuel delivery gets more aggressive as you do.

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PRESETS

DATA LOGGING

DISPLAY

most sample maps offered in industry

only data logging function in industry

choice of display

The ECU incorporates the fuel pump relay and is safely nestled behind the front number plate.

* 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 The necessary) optional KX FI calibration Kit is the same as what’s used by - setting adjustments can be prepared in advance on a PC, or done Kawasaki’s top teams around the world. Stock there are seven when connected to the ECU presets whichuser-interface can be set quickly andtoeasily, but there’s moretoyou - the kit’s is simple understand and easy use

can do if you need to. It also works as a datalogger, recording up to * The KX FI Calibration Kit contains seven preset settings that can be sixquickly hours of andengine easilydata. used to adjust the ECU to suit track conditions. The provided settings are shown below.

SETTING

DESCRIPTION

Richer fuel setting

fuelling 5% richer than stock

Leaner fuel setting

fuelling 5% leaner than stock

Advanced ignition setting

ignition advanced 3o from stock

Retarded ignition setting

ignition retarded 3o from stock

Hard riding surface setting

ignition retarded, fuelling richer

Soft riding surface setting

ignition retarded, fuelling richer

Beginner setting

engine power suppressed: ignition retarded, fuelling richer

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The fuel pump is designed to ensure a consistent supply of go-juice to the EFI even as you’re smashing berms and jumping triples.

The injectors actually supplies more fuel than the unit off the 450, because the 250 revs harder.

‌and engine updates For the 2010 KX250F, Kawasaki concentrated on performance, and made the bike one of the fastest in the field. While the biggest changes for 2011 focus on the fuel injection, Kawasaki hasn’t ignored the engine. Retained but updated is the bridged-box bottom short-skirt piston. This design features fully-flush internal bracing to make the piston stronger and lighter. The piston crown has been updated to suit the better over-rev and top-end, compression is up by 0.3 to 13.5:1 and the cylinder height reduced accordingly.

Other changes include different valve timing, increased valve lift and stronger valve springs.

Increased intake ducting and a new spark plug extending further into the combustion offset the usual loss of performance at the bottom-end associated with a switch to EFI. A 48-tooth rear sprocket replaces the 50-tooth unit on the 2010 model, and the exhaust pipe is 30mm longer to suit the new engine characteristics, but noise is actually reduced thanks to new internal baffling.

The bridge-box bottom piston has been updated for 2011. The unique mass produced design is both strong and light.

The barrel is slightly updated from 2010.

Revised muffler baffling for reduced noise.

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SPECIFICATIONS KX250YBF ENGINE Type: Liquid-cooled, 4-stroke Single Displacement: 249cc Bore and Stroke: 77.0 x 53.6mm Compression ratio: 13.5:1 Valve system: DOHC, 4 valves Fuel system: Fuel injection: ø43 mm x 1 (Keihin) Ignition: Digital DC-CDI Starting: Primary kick Lubrication: Forced lubrication, semi-dry sump Transmission: 5-speed Final drive: Chain, 50/13-tooth sprockets FRAME Type: Perimeter, aluminium Wheel travel: front 315mm, rear 310mm Caster (rake): 28.2 degrees SUSPENSION Front: 47 mm upside-down telescopic Separate Function front Fork (SFF). Fully adjustable for spring preload, compression damping and rebound damping.

Rear: New Uni-Trak (linkage type with spring/damper unit). Fully adjustable for spring preload, high and low speed compression damping and rebound damping.

BRAKES Front: Single semi-floating 250 mm petal disc with dual-piston caliper Rear: Single 240 mm petal disc with single-piston caliper DIMENSIONS Overall length: 2,170mm Overall width: 820mm Overall height: 1,270mm Wheelbase: 1,475mm Ground clearance: 330mm Seat height: 945mm Curb mass: 105.7kg (EUR/AUS/JPN/BRA) Fuel capacity: 7.2 litres Price: RRP $10,999

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NEW smooth action, low-friction Separate Function Forks NEW digital fuel injection delivers immediate throttle response NEW programmable ECU (via optional calibration kit) Factory-spec engine tuning boosts high-rev performance Updated shock absorber with dual compression adjustability Lighter handling chassis with increased rear wheel traction

Radical new SFF fork NEW

Digital fuel injection NEW

Making History: 1-2-3-4

The KX250F is the first mass-production Motocrosser to feature the radical new Separate Function front Fork (SFF) with 25% less friction than standard forks.

The KX250F’s new fuel-injection system delivers immediate throttle response, pinpoint tuning and automatically adjusts to suit track and climate conditions.

In 2010 the KX250F won the AMA East and West Supercross Lites titles and finishing 1-2-3-4 in the East Vs West SX Lites Final showdown.

Go to www.kawasaki.com.au for the latest Kawasaki motorcycles, news and dealer information Photograph depicts a professional rider under controlled conditions. Kawasaki Motors Pty Ltd endorses safe riding. Always wear an approved helmet and protective riding clothing. Never ride a motorcycle under the influence of alcohol or drugs.