The greenbacks might not be rolling in the motorcycle industry right now, but that didn’t stop Team Green from giving the KX250F motocross bike a massive overhaul for 2011. The Kawasaki R&D team was hard at work with the Lites-class racer and the KX-F has joined the fuel-injection club. Swapping the carburetor was just one of nearly 30 changes for the updated model. Plenty of internal engine mods went with the FI but the other big news is a Separate Function Fork (SFF) which puts one leg in charge of spring action and the other compression and rebound.
With such a big list of important changes, Kawasaki needed an equally impressive venue to put it on display, so what better than the National track at Budds Creek – the site of the 2007 Motocross des Nations where Ryan Villopoto slaughtered the entire motocross world on his Pro Circuit-tuned KX250F. We asked Mikey Henderson to come along for a perspective from the other side of the fence – that being the really fast side. The Colorado rider currently races a KX250F and holds his AMA Pro License for racing the outdoors. He’s also five inches shorter than our other tester at 5’6” which means his take on ergonomics and chassis are more varied as well. So, let’s dig in.
Keihin fuel injection is the big news for 2011. Of course it couldn’t just stick to the industry standard EFI moniker. Kawasaki calls its fuel delivery system DFI (digital fuel injection). Engineers basically sourced the setup from the KX450F, though it has different settings in the ECU. There is no battery as the system is charged via the enlarged stator and its 24.7mm-larger rotor. Kawi claims it takes three rotations of the crankshaft to charge the ECU, fuel pump and injector before starting. A 43mm throttle body is the same as the 450, but Kawasaki says the use of an aluminum injector provides 20% more injection capacity, which is needed for the higher-revving 250F. Despite the inclusion of a fuel pump, the KX-F still offers 1.9 gallons of fuel. The KX FI Calibration Kit works with the new system, as well as the upcoming 2011 KX450F, for detailed engine mapping and data logging. It connects behind the black front number plate.
The four-valve engine with titanium 31mm intakes and 25mm exhaust openings churns out 249ccc of displacement via 77mm x 53.6mm bore and stroke. A revised cam profile gives higher lift on the intake side and a stronger valve spring is used to match. Compression bumps 13.2:1 to 13.5:1 with an updated piston crown. The details continue right down to the spark plug which is longer and makes use of a hotter, longer-duration spark from the revised coil. The crank is now web shaped in response to a 3mm-larger rotor. Airflow is increased to the motor with a 10% larger air boot while exiting the engine it flows through a longer head pipe (30mm) and muffler with larger volume. The silencer also has a smaller diameter, perforated pipe.
Transmission ratios for second and fourth gears are revised to suit the engine delivery. The shifting mechanism is changed also so that the ratchet rotational angle is increased and the return spring has less tension.
Whatever the name, the fueling system works really, really well. As for starting, it took roughly 2-4 kicks when cold and 1-3 when hot, and our testing conditions reached 93 degrees and 44% humidity (according to a cell phone weather report). We chopped the throttle everywhere we could, smacked it open again, rolled it on and gently backed it off, hammered into the face of Budds’ stairstep double-double and came up short on big tabletops. Not once did the motor hiccup, pop, gurgle, splutter or bog. The same goes for Mikey, though he over-jumped rather than came up short, either way, the flawless performance was the same across the board.
“My favorite thing about the motor is the fuel injection,” he says regarding the multiple updates. “It has no bog anywhere. The low-end hits good, especially in first gear, but it pulled for longer in comparison to the 2010. Mid-range was really strong most everywhere, but the top end was in need of more power. It is still super-fast overall for a 250F, however, I wouldn’t mind a bit more top end on it.”
Despite his greedy wishes for more, the little KX-F had enough top end to pull our 150-pound pro over the massive uphill double in fourth gear. The other tester tips in around 180 lbs, and though he was far from hucking the death jump, the Kawi had enough muscle for him in every situation as well. This is a tremendous motor.
AMA Pro Racing is constantly updating (lowering) its sound limits and the Kawasaki brass say the ’11 model meets the upcoming 94 dB limit. Umm… we’d be surprised. Granted, we were in the valley at Budds Creek and were the only bikes on the track, so sound was reverberating and there was nothing to compare it against, but the KX250F is still loud as hell and raspy like we’ve come to expect from green bikes.
There was no beef with the new tranny or final gearing. The five-speed shifts quickly and easily and the clutch pull is light and without fade. Mike spent more time in the saddle and was able to discern a few subtle characteristics.
“The clutch adjuster is so easy to turn this year, initially I thought it was broken,” says Henderson. “There is no hot start in the way this year, which is an improvement. The new gearing felt good, second gear could pull to the moon and fourth was huge as well. I really like the new setup, but I did notice it felt harder to shift than the older models from second to third.”
Top: One fork controls the spring and the other
manages damping circuits. Middle: The spring
preload adjustment. Bottom: Blue anodized fork
caps look trick and are simple to use.
Kawasaki still uses Showa suspension components for the 250 and Kayaba on the big bike, but the quarter-liter gets a totally new fork for 2011. The system is split so that one fork leg (right) handles the spring and preload while the other (left) controls compression and rebound damping circuits. This technology isn’t necessarily new, but it’s the first time a manufacturer has made it available on a production motocross bike.
Everyone knows that you need to adjust the preload tension on the shock to get the proper ride height (or they should), but doing likewise with the front end has always been a major undertaking, involving removing the fork, busting into the internals and adjusting collars. Basically, it’s not commonly done – that all changes with the SFF system.
The right fork houses the spring, which is longer and stiffer than the older version, and the rod assembly is oversized as well. A small amount of fork oil resides inside for lubrication purposes only. A blue-anodized external hex-head offers 60 clicks of preload adjustment. Six clicks equals one full turn, and one full turn equals 1mm of preload on the spring – therefore you have 10mm of fork preload to mess with. Factory settings put the preload at 22 clicks from full out. Changing spring rates is half the work and can be done without removing the fork from the bike. With only one spring, Kawasaki claims a 25% reduction in stiction. The upper fork tube is Kashima coated and the lower gets titanium oxide coating, both with the intention of freer movement and longer durability.
The left fork controls rebound and compression damping with standard clickers on the bottom and top of the fork leg, respectively. The single damping piston is larger and changing clickers is easier now that you don’t have to match the settings on each fork. Kawasaki claims that suspension work should be simpler and potentially cheaper since only one fork could potentially need service. A revalve would only require half the shims, half the oil, etc. That very well may be the case, but we’d like to know if that means the fork is going to need service twice as often. Only time will tell and it’s up to the aftermarket companies to determine if they will charge less for their services.
The Uni-Trak shock isn’t nearly as mind-blowing as the front end, but new internal damping pairs it with the updated fork. Riders can still tune the 12.2 inches of travel for spring preload, high-speed compression, low-speed compression and rebound and the shock body comes with a Kashima coating.
The best feature about this new setup is the adjustability. There’s nothing else like it on the market and having the capability to set preload on the fork in addition to the shock is amazing. So how do you even start? The first step is to adjust the rear sag as usual; Kawi recommends 100-104mm. Then you move to the fork where measuring uses the same technique of pulling from the axle to a fixed point on the upper fork tube or triple clamp. First measure it unloaded on a bike stand and then have the rider sit normally in the saddle on level ground. When the rider straddles the bike, Kawi recommends 45-55mm of sag on the front end. From there you can tweak the clickers to meet your needs for particular track settings.
The first thing Kawi wanted us to do was crank it down all the way and then back off the preload entirely, just to see how drastic the difference is. It’s not a gimmick, the bike behaves completely different. Tightening the spring to full capacity keeps it very high in the stroke so the front end doesn’t want to turn. Our slower rider actually preferred the fork movement in this state, but it wasn’t worth having a bike that refuses to find a rut. Backing off the tension lets the fork be very soft on the upper end of the stroke, meaning it drops the front with ease and makes the bike handle very quickly. Our preferences were both on the softer side of the stock setting.
Changing the amount of preload on the fork is simple and it makes a huge difference in handling. Both of our riders preferred to back the clicker slightly off the stock setting which gave the front end more traction.
“With the way the new fork is, they seem very much the same as last year’s until you start making adjustments. Just one click makes a difference,” notes Henderson. “When I first got on the bike it was too soft on the compression, but rebound was ok. By the end of the day we had tried moving clickers all the way in and out on both. At first it would bottom out and make a harsh landing off the big stuff, but after the changes were made, the stock suspension worked great.
“We played around with the new adjustable preload feature also and it was crazy to feel the difference on how much 3mm shorter made on the front end going into corners. We were able to make it to where the forks had the feel of a longer stroke all the way through. We found a good race feel at three clicks stiffer on compression, two on rebound and 1.5mm shorter on the front preload.”
Big jumps are no problem for the suspension. Our pro tester opted to stiffen everything up a bit and was happy for the rest of the day.
Whether it’s a lack of a second spring or perhaps less total oil volume, the fork does seem to have a lighter motion. We both noted how the front end moves through the stroke much more willingly than older models. The slick action makes changing the adjustable features more pleasurable in that we felt like it was easier to make progress with the tuning.
Kawasaki’s press material states that the new suspension is targeted at “race-experienced riders” but that doesn’t mean that entry-level or lesser skilled pilots won’t gain from the new technology. Our testing duo proves that pros and Joes alike can have success finding a better balanced package. And since it’s so easy to mess with, riders will be more apt to try different settings and truly learn how their suspension works best under different riding conditions.
As for the shock, it definitely gets overshadowed by the spiffy new front end, but it goes about its job quietly and effectively. Heading into the braking bumps at speed brought a small hop as it would from any machine, but we didn’t experience extreme swapping or unsettling all day. Henderson felt that he could get the rear to squat by changing fore and aft preload settings which made the bike handle to his liking in the corners.
An aluminum perimeter chassis uses forged, extruded and cast components. Geometry involves 28.2 degrees of rake and 4.7 inches of travel with a wheelbase of 58.1 inches. Fork offset drops from 23.5mm to 22.5mm. Engine mounting brackets have switched from aluminum to thinner gauge steel, a move prompted by the personal tastes of Reed and Villopoto during race testing. The swingarm is longer to accommodate for a sprocket change. The countershaft gear still has 13 teeth, but the rear sprocket jumps from 48 to 50, adding two links to the chain length.
It was pretty obvious that Mike had no major qualms with the handling. Henry Hill and the rest of Budds Creek was a big, rolling playground.
Watching Mikey scrub the top of Henry Hill was a pretty good indicator that the 250F is easy to toss around. Nothing caught our boots or hindered us in any way. Bodywork allows for easy contact with the machine and the rider triangle fit both of our testers without problem. Mike rotated the bars a little to get them closer.
“Kawasakis have always been great handling bikes. At Budds Creek, there is every type of riding from huge jumps to tight corners, ruts and bumps. I was able to pick any line on the track and make the bike stick. The bike felt stable in rough sections at high speeds, but it also gave the feel that i was going to be able to drag bar in a sick rut. It felt nimble in the air, as well. I particularly liked that I felt I was always able to control it. I never once felt there was a place the bike handled poorly.
“The 250 always feels shorter from rear fender to bar,” continues the 5’6” rider who also spends time on a KX450F. “I felt I was able to attack on rough sections and it wasn’t bad to dive into a corner. I really felt like I could throw it around. The bar position had to be brought back for me and sometimes I felt there was a tendency to get headshake on the rough sections. The peg height is great and I never had a problem with a foot getting ripped off in the ruts.’
The headshake issue could have been a result of the lessened offset or improper fork preload, but having the ability to change that dynamic is amazingly helpful. Though far less stylish and aggressive at the controls, our larger tester appreciated the handling as well. The bike had been ridden previously and the seat was broken in nicely; both riders noted the level of comfort available from the 37.2-inch high perch with new cover material.
Kawasaki uses petal-style disc rotors and Nissin calipers to haul down the speeds. A 250mm semi-floating front caliper has two pistons while the single-piston rear latches to a 240mm rotor. It’s the same setup as last year.