September is a pretty exciting time of year in the motocross world, by now the specs have been released on most new models and at least one of the big manufacturers has claimed the Early Bird status and landed their new offerings in dealerships Australia wide.
This year Kawasaki has set the pace, with the early release of the KX250F, and to make things even more exciting, the 2017 model is an all-new machine from the wheels up.
Lighter, faster, slimmer
… is the tagline Kawasaki is using to promote its new 250, and sure, it may seem obvious making the bike lighter and faster will improve its overall performance but if you take a look at the engineering behind the new KX it’s pretty clear Kawasaki didn’t just bolt on a few new fast parts and assign the KX250F to the latest fad diet program.
Beginning with the faster updates to the KX250F, the entire engine intake system has been revised.
The engine has been straightened up and now sits seven degrees more upright, with the throttle body, dual fuel-injection and air filter positions raised to allow for a straighter, and more downdraft-shaped intake.
The dual fuel-injection system has its changes as well, with a new downstream (closest to the engine) injector, featuring more holes and a finer, wider spray.
This is said to have increased power in the low-mid RPM and added throttle response.
The upstream (further from the engine) injector remains unchanged.
The cylinder offset has been changed, and is now 3mm further forward, with a new honing technique used called plateau honing, which leaves a smoother surface finish on the bore of the cylinder.
Both of these improvements are aimed at reducing mechanical loss, providing increased efficiency and power output.
A new ‘race replica’ piston replaces the previous design, which features a molybdenum coating instead of tin plating to reduce friction.
Further updates to the piston include design changes to the bridged box bottom and pin position to increase strength while shaving weight at the same time.
The crank design changes slightly from the 2016 design too, with a new web design shape increasing the balance factor to around 70 per cent, which is claimed to be on par with the factory race engines.
The new crank contributes to reduced engine vibration and smoother power at higher RPM.
Making the KX250F lighter and slimmer was just as in-depth for Kawasaki’s engineers, with a complete chassis re-design being in order.
The steering stem shape, shock mounting tower design and swingarm mounting area have all been completely revised to increase rigidity and give the chassis a 6mm slimmer profile.
The front ‘downtube’ section of the chassis is now a made from a forged section at the front and a cast section at the rear where previously it was a single extruded piece design.
All components are still aluminium, however the manufacturing process for each piece changes the outcome once the chassis is fully assembled, making the overall design stiffer and lighter.
The swingarm from the KX450F comes directly across to the 250F with no changes at all, its a more rigid aluminium design, with the new construction saving almost 200 grams.
New bodywork on the KX not only gives a fresh new look with stylish in-mould graphics, a first for Kawasaki, but the redesigned seat and 6.4L fuel tank give a slimmer, flatter riding position.
The radiators are re-positioned lower and are 20mm narrower to allow even more room for the rider to move around on the bike.
To match the updated chassis, new suspension settings have been added at both ends.
The Showa Single Function fork receives a firmer spring rate and new valving, while the Showa rear-end receives a softer spring rate with new valving.
This means less ‘pitching’ from the back-end while under load, and increased stability at speed.
Remaining unchanged on the KX250F are the Renthal handlebars, adjustable handlebar position mounts, adjustable footpeg height mounts, Black wheels, and oversize 270mm front disc.