WE ALL RIDE FMF’S KX500/KTM 250SX TWO-STROKE RACER

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There is a recurring dream that persists in the motocross mind? the dream of building the ultimate racing weapon. Lots of lunch hours and bench-racing sessions are filled with discussions about building the perfect motocross bicycle. The conversation always focuses on getting a chassis that is light, narrow little. The frame has to be sourced through readily available units, and, most important, the ultimate race bike needs the most powerful, yet manageable, powerband that the sport’ s engineers have ever created.

One important caveat in the dream-bike scenario is that the bicycle cannot have a 450cc four-stroke motor. Why would it? Four-strokes are readily available and therefore not dreamy enough. That means the ultimate motocross bike would most likely be powered by a 500cc two-stroke motor. It is the rarest of engines, and it also makes the most torque and competing horsepower. It can be detuned or hopped-up with ease, and it is lighter than contending 450cc four-stroke engines.

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The best project bikes are the ones that look like they rolled from the factory. FMF’ s KTM/KX500 crossbreed fits the bill.

A COUPLE OF YEARS AGO, THE FIRST CHOICE WOULD HAVE BEEN A CRF OR KX250F FOUR-STROKE FRAME. IT WAS CONSIDERED THE EPITOME OF MODERN DESIGN.

Okay, with the basics of the dream bike down on paper, it is time to make some decisions about the frame and motor package.

(1) Frame. The very first hard decision is choosing between an aluminum Delta-Box frame through an existing four-stroke and a chromoly steel KTM chassis. A few years ago, the very first choice would have been a CRF or KX250F four-stroke frame. They were considered the particular epitome of modern design. But , lately, KTM’ s oval-tube, chromoly steel frame has begun to overshadow the particular rigid Delta-Box design. Not only really does KTM’ s steel frame handle very well, it has more room for your engine of choice and can be cut, chopped and welded with ease. Choice made? 2013 KTM 250SX frame.

(2) Powerplant. Choosing a 500cc two-stroke engine is as simple as ordering Chinese food. You select one through column A or one through column B. In column The is the venerable Honda CR500 motor, and in column B is the equally venerable Kawasaki KX500 engine. The particular Honda CR500 engine was final produced in 2001, but parts can easily be bought, and it has a great reputation left over from the days as the engine of choice associated with Jeff Stanton, Jean-Michel Bayle, David Bailey and Rick Johnson. On the other hand, the last KX500 engine rolled off the assembly line in 2004 and is actually a better all-around powerplant compared to CR500 engine. It has a broader powerband and more controllable output. The main reason it gets less publicity compared to Honda CR500 engine is because the particular KX500′ s suspension, layout and ergos were less suited to motocross than the Honda’ s. Decision produced? 2004 Kawasaki KX500 engine.

The only welding required to squeeze the particular 2004 Kawasaki KX500 engine into the 2013 KTM chassis was to the bottom motor mount.

Not every driver has the same dream, but the MXA wrecking crew ran into 2 industry powerhouses who did share the same vision and were doers more than dreamers. A year ago, FMF’ s i9000 Donny Emler and former 250 World Champion Danny LaPorte experienced the same conversation we just talked about. And, unlike most bench racing enthusiasts, they decided to make the dream a real possibility. Danny had raced the Baja 500 for Team Kawasaki and believed that a KX500 engine could still win Baja if it were in the right chassis. Donny and Danny decided to go with the 2013 KTM 250SX chassis, plus its suspension, running gear, wheels and brake systems. They chose it because they enjoyed the way it handled, and they enjoyed that the chromoly steel could absorb some of the heavy vibes of the KX500 powerplant.

IT DIDN’ T HURT THAT WILL DONNY EMLER HAD BUILT HIS REPUTATION BACK IN THE GLORY DAYS SIMPLY BY SWAPPING OUT HONDA AND PENTON PARTS TO BUILD GREAT 125cc COMPETITION BIKES.

Once they chose the engine and the chassis, the daunting task of putting the two together began? except that it wasn’ t a daunting task. Danny LaPorte says, “ When we very first looked at the Kawasaki engine as well as the KTM frame, we didn’ capital t think it would fit in there, yet we were wrong. The first time we fixed our rebuilt KX500 engine into the KTM frame, we realized it had been going to be the easiest engine swap ever. ” It didn’ t hurt that Danny’ s partner on the project, Donny Emler, had built his reputation back in the glory times by swapping out Honda and Penton parts to build great 125cc race bikes.

Uncle Donny knows a thing or two about exhaust plumbing, so shoehorning a big expansion holding chamber in was no sweat.

PUTTING THE KX500 ENGINE INTO THE KTM 250SX FRAME WAS EASY (FOR THESE GUYS)? JUST A THREE-STEP PROCESS.

Step one: To have the KTM swingarm pivot bolt with the Kawasaki KX500 engine cases, the particular cases were center-bored. Emler elected to bore the cases just a couple of thousandths larger than the KTM revolves bolt to get as snug the fit as possible. The swingarm revolves bolt is the only fixed placement on the engine swap. To fall into line the countershaft sprocket and rear KTM sprocket, a 6mm spacer was machined to push the particular engine over to the side. This was a simple task, because the KX500 engine instances were narrower than the space between your KTM frame’ s down bed rails.

Step two: To get the crank as low as possible, Donny and Danny made a decision to do whatever was necessary to get the engine cases as low as possible within the KTM frame. To accomplish this, they notched the frame cradle tubes beneath the engine and welded chromoly tubes into the notches to accept the bottom motor-mount bolts. They went as low as they might go and still have tubing still left under the frame cradle, but the actual position was determined by simple reasoning. They put the bottom motor-mount bolts within the spot that made the imprinted Kawasaki logo on the clutch include level. Additionally , they had to damage one frame cradle tube to obtain access to an engine-case bolt.

Step three: The final task was to fabricate new front motor-mount plates and a head stay. The rest of the build was basic problem-solving for the coil, intake tract, reed valve and change lever. Danny and Donny insist that the engine swap was simple as pie and, by engine-swap standards, this is true. But , no mechanic ever tells you the whole story. They conveniently forget their worries and head scratchers.

IT WAS REALLY DANNY LAPORTE WHO PUSHED FOR THE KAWASAKI POWERPLANT, BUT HE WASN’ Capital t LOOKING FOR MORE POWER; HE KNEW IT WOULD HAVE MORE THAN ENOUGH IN STOCK TRIM.

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You haven’ t flown until you fly Atmosphere 500. Big doubles are no trouble when you have a 500cc two-stroke under you.

It was really Danny LaPorte who pushed for the Kawasaki powerplant, but he wasn’ t looking for more power; he knew that it would have more than enough in stock trim. Instead, the duo tried to detune the particular KX500 a little bit with an intake atmosphere boot that had a little less volume for better throttle reaction and a touch less top end. The particular compression ratio was left stock, as was the 40mm carburetor.

The spigot was moved.

Getting an exhaust tube built was no problem, because Danny LaPorte knew a guy who owned a pipe shop. Luckily, FMF builds exhaust systems for the Service Honda CR500AF aluminum-framed bikes. So , Donny started with some CR500 cones, custom-rolled a few more, and made a very technique lowboy KX500 pipe that match like a glove. The only problem? and it also wasn’ t a small one? was that the water spigot on the right part of the cylinder was directly within the path of the pipe. Now, you may think that a famous pipe builder might just weld up a new tube to work around the spigot. Not so! Instead, Donny moved the water spigot over 2 inches and covered in the old spigot hole. Problem solved. For a muffler, Donny selected the KTM PowerCore silencer, because it might mount right up to the KTM 250SX subframe.

Although you wouldn’ t know it by the appears of it, this bike was designed to race the Baja 500. However a funny thing happened along the way to Mexico. Danny started operating it at local motocross songs to shake out the bugs, as well as the more he rode it, the greater he liked it. So , Donny and Danny decided to use it as a motocross bike and start on another KTM/KX500 hybrid for Baja.

JODY PLUS DONNY TALKED ABOUT THE BIKE FOR SOME MINUTES, AND THE NEXT THING YOU KNOW, THE BIKE TRADED HANDS. DONNY OFFERED HIS PROJECT BIKE TO MXA ON THE SPOT.

This is where the MXA wrecking team came in. We were parked next to Danny and Donny at Glen Helen on a day when they were trembling down their project bike. Jody and Donny talked about the bicycle for a few minutes, and the next thing you know, the bike traded hands. Donny gave his project bike to MXA on the spot. Jody sent three different MXA test riders on it immediately to iron out some suspension and jetting issues. From that moment on, MXA started racing the KTM/KX500 every weekend. Here is what we learned (and we kept Donny’ s KX500/KTM for almost four months, raced this at the World Two-Stroke Championships and used it to scare young guys).

The KTM chassis had a hydraulic clutch lever, so the Magura hydraulic clutch actuator was added to the KX500 engine.

You might think that the 500cc two-stroke engine would be brutally powerful, or that it would loop over backwards with the slightest twist of your wrist. You might also be led to believe by the current crop associated with pantywaists in the sport that you can proceed faster on a 450 four-stroke than the usual 500 two-stroke. Not true. The KTM/KX500 makes a lot of power, but it places that power to the ground in such a way that even a Novice could go quick on it. Really fast! It is accurate that you could get into trouble if you obtained carried away with yourself, but upon long straights, wet loam, heavy sand or big uphills, nothing can touch a 500cc cigarette smoker.

When you ride the particular KX500 properly, it feels like it posseses an automatic transmission. The MXA check riders didn’ t have to do completely shifting, and clutch action was limited to pulling it in whenever overshooting corners (because they misjudged the speed they were traveling). In many ways, the particular KX500′ s broad, tractable and automatic powerband (it is a five-speed) allowed the riders to concentrate on picking lines, grabbing big handfuls of brake and lining in the competition on the straights.

Since the engine was stock, all of us did most of the tuning with the rear sprocket. Our Pro test bikers wanted it geared down one particular tooth so they could get to third gear sooner. Our Novice and Vet test riders didn’ capital t like the lower gearing because it produced the KTM/KX500 more abrupt in second gear. There were even some test riders who preferred to gear it up to make each gear mellower and longer.

AS THE YEARS GO BY, IT IS HARDER TO FIND TEST RIDERS WITH ANY 500cc EXPERIENCE. LUCKILY, MXA KNOWS A BUNCH OF FORMER NATIONWIDE PROS WHO KNOW HOW TO USE A 500cc TWO-STROKE TO ITS FULLEST.

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With the exception of stiffer shell springs, Donny and Danny didn’ t make any changes to the stock KTM 250SX forks.

As the years go by, it is harder to find check riders with any 500cc encounter. Luckily, MXA knows a bunch of former National Pros who know how to utilize a 500cc two-stroke to its fullest. Compared to a Honda CR500, the particular Kawasaki KX500 engine is without doubt faster. The best way to control the power is by using a series of short-shifts to keep the motor in the meat of the powerband.

Every MXA test driver loved the KTM/KX500. For the more youthful test riders, which was any driver under the age of 30, this was their first experience with a 500cc two-stroke. They struggled with the power in the beginning, but once they learned that you didn’ t need to use all the energy the bike produced, they started to get in tune with the big beast of an engine. It came upon harder, pulled harder and needed a moment’ s thought prior to pulling the trigger. A 400 four-stroke might be intimidating for some, but the KX500 powerplant produces a whole new level associated with terror in the untalented or unwary.

Overall, we adored the KTM frame. The bicycle handled like a dream. The brakes were awesome, and the layout was rider-friendly. Donny installed an aftermarket Magura hydraulic clutch to help the KX500 clutch pull. Since the KX500 motor was heavier than the KTM 250SX mill, the bike gained 13 pounds. But , even with the extra weight, it was still lighter than the majority of 450 four-strokes and felt also lighter in motion. Donny experienced Factory Connection add stiffer shell and shock springs to compensate for your engine’ s weight and energy, but the WP forks and surprise were left stock.

Choosing the best muffler was no problem. FMF went through their KTM two-stroke inventory and voila!

The truth is that if KTM built this particular bike, with a KTM 500cc motor in place of the Kawasaki powerplant, it would sell. It’ s a fun bicycle to ride, a blast to rise hills on and a guaranteed holeshot at any track in America. And, because it is as close to a production 500cc as anyone has ever come, it doesn’ t have any kind of compromises. It lives up to the motocrosser’ s dream? it is light, thin, compact and powerful. Oh yeah, simply by engine-swap standards, it was also simple to do.


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