WE RIDE CYLINDER WORKS’ BIG-BORE KAWASAKI KX269F

It’s easy to think that Cylinder Works is pandering to cheaters with their line of big-bore engine kits. There is no doubt that cheaters are drawn to what Cylinder Works has to offer, but, in truth, most big-bore engine kits go to riders who are not bound by displacement rules (Vets, play riders and offroad racers). However, there could be just a hint of pandering to cheaters in that you can’t tell a 269cc Cylinder Works cylinder from a stock-bore OEM cylinder. (They even put the same casting numbers on their jumbo cylinders.)

The Cylinder Works KX269F kit is unique in that it is designed to fit on the 2012-2014 dual fuel-injector Kawasaki KX250F. With an 80mm bore (3mm larger than the stock KX250F’s 77mm bore) and the stock stroke, the Cylinder Works KX269F bore-bore kit actually produces 269.42cc. The companion parts to the Cylinder Works casting are a Vertex piston and Cometic gasket kit.
 

When you go big you gain horsepower, but lose some of the engine’s flexibility. We gained midrange, but lost top.

This is one sweet deal. For $599.95, Cylinder Works supplies a purpose-built cast cylinder (that has been nickel-silicon-carbide-plated), 80mm forged Vertex piston and all the gaskets necessary to slip this sleeper cylinder onto your KX250F. No machining. No drilling. No exotic regimens. Just replace and go. At least, we wish that were the case. Unfortunately, it isn’t that simple. The fly in the ointment is Kawasaki’s creative dual fuel injection. When we tried this 269cc kit on our 2011 fuel-injected Kawasaki KX250F, it ran without a hiccup (and we even tested the 269cc kit on the Keihin carb-equipped Yamaha YZ250F without problems). We had no hassles with single injectors or FCR carbs, but Kawasaki’s new dual fuel ignition didn’t like going big.

MAKING SENSE OF THIS

To make sense of this, you need to know how dual fuel injection works. In 2012, Kawasaki equipped the KX250F with two separate injectors. The 2012-13 KX250F’s second injector is located inside the air boot. Both Kawasaki injectors have the same output capacity. Only the first injector, in the throttle body, is running up until 7000 rpm. Then, at 7000 rpm, the upstream injector in the air boot kicks in and gradually increases fuel delivery, while the first injector gradually tapers off. When the bike is running wide open, only the upstream injector is working. Dual injectors make CPU programming more critical. The two injectors must function together seamlessly to optimize fuel delivery. When several race teams tried using a secondary injector simultaneously with a downstream injector, it didn’t work. The secondary injector needs to come into the action when the engine rpm is high enough to take advantage of it. The extra time it takes for the upstream injector’s fuel to reach the combustion chamber must be taken into consideration.

When we tried to run our Cylinder Works KX269F with the stock 2012-13 Kawasaki mapping, it popped, banged and sputtered. We were confused. This kit had performed flawlessly on the single-injector 2011 KX250F, but wouldn’t work on the 2012-13 dual-injector model.

It soon became obvious that the bigger piston translated into a bigger combustion chamber. The larger combustion chamber meant more air volume, which meant that we would need more fuel. Luckily, with modern ECUs, it is possible to increase the amount of fuel that the injectors deliver. So, with the help of Tom Morgan, we developed a new fuel map that increased the amount of fuel to keep the engine from running lean. On a side note, carbureted engines do not need to artificially produce more fuel because carburetors function via a vacuum in the intake tract. If you draw more air into the engine, the carb will pull more fuel out of the float bowl to compensate.

In short, to run the Cylinder Works KX269F big-bore kit on your 2012-13 Kawasaki, you must reprogram the ECU (just the fuel side, not the ignition map). Unfortunately, Cylinder Works will not provide black boxes or reprogram existing boxes, but they will supply the map. It is up to the buyer to get his local shop or friend with a programming tool to put in the new fuel map.

SHOP TALK: PIECE BY PIECE

For $600 Cylinder Works turned our KX250F engine into a KX269F. It would have been a simple project except for the mapping required on the dual fuel injectors. Without reprogramming, you couldn’t get the KX269F to run.

Although you can just bolt the cylinder and piston onto your stock KX250F, we decided to go a couple of steps further by changing out the cams. We elected to run Hot Cams Stage II intake ($179.95) and exhaust ($199.95) cams. There is no secret here. When you big-bore a 250cc four-stroke, you get a massive amount of low-to-mid power, but tend to lose top-end because the big piston just doesn’t push through the air as easily as the smaller one. By changing cams to Hot Cams’ new cam sets, we hoped to mitigate the loss with increased torque at around 9400 rpm.

We also ran an FMF Ti Factory 4.1 exhaust with a MegaBomb resonance chamber. It’s generally assumed that if you are racing a 2012 KX250F, you already have an aftermarket exhaust system. We didn’t, so this was a logical mod for the MXA wrecking crew to make whether we big-bored the engine or not.

TEST RIDE: PUNCHING BIG HOLES IN THE AIR

This is what a boatload of torque can do to a berm. We geared the KX269F lower for slow riders and taller for fast riders.

Step one: Once we were finished with the mechanical parts of the Cylinder Works KX269F, the first step was to take it out for a photo shoot. This is a quick and easy way to break in the engine, get the photos shot (while the bike is still in one piece) and establish a criteria for what we need to change on the setup.

Step two: Race it. As a rule, we have two or three different test riders race a test bike on its maiden voyage (then let the rest of the test ride it once we iron out the bugs). This gives us sufficient feedback from a wide range of riders. It also gives us a base to work from.

Step three: Consult the dyno. We ran the stock 2012 KX250F a week earlier to be sure that we had a good baseline. The stocker is impressive, so impressive that we never really thought of it as a candidate for a big bore?largely because it pumps out 39.55 horsepower, has an awesome power curve and has top-end over-rev that is mated to constantly increasing power. The 2012-13 Kawasaki KX250F has the best 250cc four-stroke engine we have ever tested. The bar was set very high for the KX269.

This is what a boatload of torque can do to a berm. We geared the KX269F lower for slow riders and taller for fast riders.

The Cylinder Works KX269F pumped out 40.80 horsepower at 10,800 rpm (using a 2012 engine). That was a healthy 1.3 horsepower at peak in favor of the KX269F. Additionally, the power below peak was a slam dunk for the big bore. The Cylinder Works engine made two horsepower more at 8000 rpm, 2-1/2 more at 9000 rpm, two horses at 10,000 rpm and 2-1/4 at 11,000 rpm. These are great numbers and exactly what you would expect out of a big-bore engine.Where the dyno chart wasn’t as rosy was at high rpm. From 10,800 rpm on, the big-bore KX269F started to fall off, and by 12,000 rpm, the stocker caught and passed it. At the point where the stock KX250F engine peaked, it was making 1-2/3 more horses than the Cylinder Works KX269F. This was also no surprise. Big bores don’t rev as well as stockers?and there is little you can do about it.

Step four: Analyze it. On the track, we found ourselves being limited to 10,800 rpm. Yes, the KX269 would rev past 10,800, but that was a false top that didn’t reward the test riders with thrust. Going to the rev limiter actually slowed the bike down when compared to shifting at or slightly below peak.

Although test riders like to complain, they were more than willing to take advantage of the extra horsepower in the midrange and use it to the fullest. From idle through peak, the KX269F made more power than the stocker. The stocker’s only advantage was that it revved free. It revved high, and it made power all the way to 12,800 rpm.

We had some gearing issues that ran afoul of the ignition mapping?which, although it allowed the KX269F to run, didn’t seem to be perfect. When short-shifted, the KX269F wanted to bog and required a deft touch of the clutch to keep it percolating. Some test riders chose to downshift for tight sections rather than risk having the engine bog, while others opted to change the rear sprocket to suit their riding styles or tracks. We geared taller for faster riders and tracks, and lower for tighter tracks and slower riders. This way the fast riders could stay in a gear longer, while the slower riders could get to a taller gear sooner. Either strategy worked very well. We would expect better fuel maps for this engine once it gets into the hands of more tuners.

VERDICT: WHAT DO WE REALLY THINK?

In a world dominated by racers, the Cylinder Works KX269F kit would only appeal to cheaters. That, however, is not the modern reality of offroad riding. Thanks to the popularity of professional practice riding and the growing number of Vet racers and play riders, the market for a big-bore kit is not limited to the larcenist.

For a reasonable price, a KX250F owner can gain horsepower, midrange and torque without the downsides of high-compression pistons, head porting or exotic DLC-coated buckets. Going big may seem rudimentary in the world of high-tech tuning, but it gets the job done.

For more information, go to www.cylinder-works.com or call (515) 251-4070.