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For 2019, Kawasaki revamped the KX450 to rave reviews, with a new chassis and engine, and the addition of electric start. David Pingree was our main test rider back then, and he absolutely fell in love with that bike, even thought he admitted he had not really liked the feel of Kawasakis before that.
In 2020, the KX250 (a four-stroke, as Kawasaki dropped the F off the name as of its 2019 models, read more below) got a redesigned engine and more power, but retained the previous-generation chassis. This morning, Kawasaki has introduced its 2021 KX motocross line, and the KX250 now gets a full redo, based heavily on that newer 450 platform. It not only updates the look and feel of the bike, but also adds electric start to the 250 for the first time. Plus, Kawasaki has made more updates to the engine, promising even more power.
Kawasaki says the new frame offers a better overall rigidity balance, and while many of the parts are common with the KX450’s frame, the cast parts like shock tower mount and engine hangers were designed specifically for the needs of the KX250. The swingarm is shared with the newer 450.
The engine features a revamped piston and cylinder head. The flatter piston works with a redesigned combustion chamber and a new production process on the intake and exhaust ports to further boost power. The rod is longer and cam timing is changed. Kawasaki is specifically touting more revs with the engine, both with an increased RPM limit, and also more power at those high revs. Plus, the engine now features electric start and a coned disc-spring within its hydraulic clutch.
Less changed is the suspension, but that’s not a problem because the KYB forks and shock have been well-received already. It will be interesting to see how this meshes together once the bike is on track. We expect to have our man Kris Keefer on the spot with an intro evaluation when Kawasaki is ready to roll the new bike out to the track.
As for the 450, changes are fewer but it hasn’t been left alone. Kawasaki is touting a new dry film lubricant on the piston skirt to reduce friction, and major clutch changes, including larger plates (139 mm to 146) and a new coned disc-spring for better feel with the hydraulic clutch.
The 250 is the real star of the 2021 show for the KX motocross line, however. Here are all the details from Kawasaki’s press release. And yes, these bikes do no longer have an F at the end of their model designations. We know, pour one out for the old two strokes, but Kawasaki no longer needs to call it a KX250F when there’s no longer a “regular” two-stroke KX250 in the lineup.
Despite the 2020 KX250 already benefitting from a significant power increase thanks to its adoption of finger-follower valve actuation, the engine of the 2021 KX250 has received additional changes to raise peak power even further and enable an even higher rev limit, while significantly increasing low-mid range performance.
Tuned to best suit race-experienced riders, the 249cc liquid-cooled, four-stroke engine focuses on more top-end revs thanks to improvements gleaned through Kawasaki’s factory racing efforts.
The 2021 KX250 becomes Kawasaki’s first electric start 250 motocross bike, which is activated by the push of a button located on the handlebar near the right grip, making starting easy and convenient. The ability to restart the engine quickly can mean the difference between keeping your lead or having to fight your way through the pack under intense race situations. A lightweight, compact Li-ion battery helps keep weight down, as does an automatic centrifugal decompression system fitted to the exhaust cam, which lifts one exhaust valve to facilitate starting.
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In addition to electric start, the 2021 KX250 also becomes Kawasaki’s first 250 motocross bike equipped with a coned disk-spring hydraulic clutch. The new high-capacity coned disk-spring clutch offers a more direct feel and an easier pull for lighter lever action, reducing fatigue while on the racetrack. The use of coned disk-spring contributes to lighter clutch actuation when the lever is pulled in, and a wider clutch engagement range, which facilitates control. In order to promote clean separation and help reduce drag when the clutch is pulled in, the friction plates were designed with offset segments. The hydraulic clutch is designed to provide a more consistent feeling through minimal change in clutch play as the clutch heats up during heavy use.
Utilizing the finger-follower valve actuation – a valve train designed by Kawasaki’s World Superbike engineers – helps achieve a high rev limit and allows for the use of more aggressive cam profiles, which contributes to high rpm performance. A diamond-like carbon coating on the finger followers helps protect against wear. Complementing the aggressive cams are large-diameter intake and exhaust valves with high lift, which flow more air and contribute to strong power. The processing for the intake and exhaust ports has been revised with a new, larger-diameter angle that contributes to increased performance. The cams benefit from a thin and highly durable gas soft-nitride treatment to reduce wear and increase high RPM reliability and the exhaust cam timing has been retarded 3º for better engine performance. Lightweight titanium valves reduce reciprocating weight and offer high rpm reliability, while the valve springs now feature a higher spring rate to match the higher rev limit. The addition of a three mm longer connecting rod decreases lateral force on the cylinder walls as the piston moves up and down, helping to reduce mechanical loss and improving reliability. The cylinder is offset three mm forward, reducing mechanical loss and increasing engine performance. A cylinder head mounted cam chain tensioner adds to the KX250’s dependability by offsetting the increased loads from the aggressive camshaft and high revving engine.
A plateau honing process of the cylinder bore results in a smooth surface with good oil-retention. The smooth surface also helps to reduce mechanical loss and improve power. A revised combustion chamber design and a flatter piston crown contribute to increased performance. The high-performance piston features the same design used by Kawasaki’s factory racers and contributes strong performance at all rpm. A short skirt, reinforced external ribs and the use of a bridged-box piston, featuring internal bracing, allow for a lightweight and strong piston design. A dry film lubricant coating on the piston skirts reduces friction at low rpm and helps with the piston bedding-in process.
To reduce weight, an update has been made to the crankshaft web design and the pressure balance has been revised inside the crankcase, adding to the engine’s increased performance. Low-friction plain bearings on the crankshaft pin help reduce mechanical loss and lift overall performance. For strengthening of the transmission, axle spacing has been revised to match the increased engine output. Along with matching the revised axle spacing, shape-optimized gears contribute to weight reduction.
The airbox construction features a shorter, tapered intake funnel, contributing to increased high RPM performance. The KX250 was the first production motocross bike with dual injectors an injector downstream of the throttle valve that is tasked with delivering a smooth, instant response, and a second, upstream injector located close to the airbox for a significant contribution to engine output at high rpm. The exhaust system length helps increase high rpm performance and the hydro-formed joint pipe features a reverse taper design. A large throttle body flows a great volume of air and provides a boost in high rpm performance. Adding to Kawasaki’s engineering efforts for optimized airflow is the positioning of the intake duct for a straight approach for intake air. The downdraft-style intake routing increases the intake air’s approach angle into the cylinder, improving cylinder-filling efficiency and increasing the engines power.
Contributing to the race-winning engine characteristics, the digital fuel injection system of the KX250 features a coupler package that has set the industry standard. Each KX250 motorcycle comes standard with three different couplers, easily allowing riders to select pre-programmed fuel injection and ignition mapping to suit their riding style or track conditions. The four-pin DFI® couplers select maps that are designed for standard, hard or soft terrain settings. Changing the engine map is as simple as connecting the coupler cap of choice. For riders looking to fine tune their ECU settings, the KX™ FI Calibration Kit (Handheld) is offered as a Kawasaki Genuine Accessory and provides access to the fully programmable ECU. Used by the factory race teams, the handheld device eliminates the need for a trackside laptop and gives riders the ability to create custom maps for precise adjustment of fuel and ignition settings. The user-friendly device can store up to seven preset maps and is PC-compatible.
The launch control system of the KX250 motorcycle is a major advantage and favorite for riders who are focused on getting to the first turn ahead of their competition. The push-button activation retards ignition timing in first and second gear, helping maximize traction on slippery surfaces like concrete starting pads and put the bike’s potent power to the ground. Once the rider shifts into third gear, normal ignition mapping immediately resumes and full power is restored.
The KX250’s new slim aluminium perimeter frame is based off of its KX450 counterpart and with lightweight, nimble handling, and slim ergonomics in mind. Its design is a lightweight construction composed of forged, extruded, and cast parts. The new frame offers a better overall rigidity balance, and while many of the parts are common with the KX450’s frame, the cast parts like shock tower mount and engine hangers were designed specifically for the needs of the KX250. Adding to the frame’s rigidity balance is the use of the engine as a stressed member. The steering head area, main frame rails with updated cross-sections, line for the swingarm brackets, and wider lower frame rails have all been revised and contribute to the overall rigidity balance.
The addition of a KX450 swingarm delivers the rigidity necessary to match the frame and helps to increase traction at the rear wheel. The center of gravity and key dimensions such as swingarm pivot, output sprocket and rear axle locations have all been carefully selected so that the rear tire drives the bike forward.
The KX250 is equipped with large diameter 48 mm KYB inverted coil-spring front forks that offer optimum action at the initial part of the fork stroke. The forks feature large-diameter inner tubes, enabling the use of 25 mm damping pistons and delivering smooth action and firm damping. A Kashima Coat on the forks’ outer tubes creates a hard, low-friction surface to help prevent wear abrasion on the inside of the tubes, ensuring the sliding surfaces remain smooth over time while protecting the outside against corrosion. The lubricating material in the coat contributes to smoother suspension action and a better overall ride feel. The lower triple clamp has been revised for optimized rigidity and reduced weight, while contributing to the front’s ability to absorb bumps.
In the rear, a KYB shock unit complements the front fork. The rear shock features dual compression adjustability, which allows high-speed and low-speed damping to be tuned separately. Kashima Coat on the tank cylinder helps prevent wear abrasion and reduces friction for smoother suspension action. A new Uni-Trak® rear suspension system mounts the linkage arm below the swingarm, allowing a longer rear suspension stroke. The linkage ratios have been revised, now using the same as those found on the KX450 motorcycle, contributing to both increased absorption and damping performance. Both front and rear suspension feature new fine-tuned settings that are designed to match the frame and provide increased bump absorption as well as increased traction.
Contributing to the numerous factory-style racing components on the KX250 motorcycle are petal disc brakes. Up front is an oversized 270 mm Braking® brand rotor, which delivers strong braking force and superb control. A new front master cylinder like the one on the KX450 adds to the high level of control and overall feedback found in the front brake.
On the rear, a new smaller-diameter 240 mm Braking brand disc contributes to controllability and offers optimized stopping performance. The petal-style discs contribute to both sporty looks and help deflect debris. A rear caliper guard helps protect the caliper from damage.
Kawasaki continues its unmatched commitment towards providing riders with class-leading comfort thanks to its ERGO-FIT® adjustable handlebar mounting system and footpegs to fit a variety of riders and riding styles. New for 2021 is a factory-style 1-1/8” thick aluminum Renthal® Fatbar® handlebar, a popular aftermarket part that is now a standard feature. The handlebars feature four-way adjustable mounts. The multi-position handlebars offer two mounting holes with 35 mm of adjustability, and the 180-degree offset clamps boast four individual settings to suit different size riders. The footpegs feature dual-position mounting points, with a lower position that reduces the standard setting by an additional 5 mm. The lower position effectively lowers the center of gravity when standing, and reduces knee angle when taller riders are seated.
Complementing the improved peak power and precise handling of the KX250 is sleek new bodywork with factory-style graphics that helps ensure it’s the sharpest looking bike in the paddock and further reflect its highly-tuned performance.
For 2021, the bodywork has been designed to facilitate rider movement with long, smooth surfaces that make it easy to slide back and forth. The seams between the shrouds, seat, and side covers are as flush as possible to help the rider move around on the bike. A revised design on the top of the fuel tank allows an even flatter progression from the seat to the tank, which gives the rider greater freedom of movement when changing riding position and facilitates sitting farther forward. The single-piece radiator shrouds are now slimmer where they come in contact with the rider’s legs and positioned closer to the frame. In-mold graphics result in an ultra-smooth surface and contribute to the KX250’s factor-racer looks.
Engine covers have been redesigned and are smooth in order to not impede rider movement. Helping the KX250 retain its factory-style look is a new gold finish on the oil cap and the two plugs on the generator cover, while the rims are coated in black alumite.
Kawasaki Team Green Racer Rewards return for the 2021 racing season with more than seven million dollars in contingency available for eligible KX riders. Team Green’s Racer Rewards program will be available at more than 240 events across the nation. Motocross racers will have more than $5.4 million up for grabs, while off-road riders will also be rewarded with more than $2.2 million available.