"If you spend enough time...
"If you spend enough time driving from race to race in your pickup truck by yourself, you're going to think up some crazy stuff!"
It all started with a road trip. Back in June of 2009, Journeyman racer Matt Karlsen was watching the scenery fly by on his drive home from the EnduroCross season opener in Las Vegas when he decided to build an off-road bike. Just like that. Whether this wild idea was created by Matt's tired brain just to keep him awake or not is up for debate, but either way the thought consumed Matt's brain for the duration of the drive. By the time he pulled into his driveway in Denver almost 12 hours later, Karlsen had a plan. He headed straight out to his shop and started tinkering, and four months later emerged with the bike of his dreams.
Now would be a good time to mention that Matt Karlsen is neither, by trade, a fabricator, nor is he a welder, engineer, architect or designer. Karlsen is a racer, and a pretty fast one at that. Be it at the Outdoor Nationals, EnduroCross, World Vet Championship or WORCS, it's not uncommon to see #940 roosting around the track in a respectable qualifying position. He's also an accomplished Triathlete, and has experience testing for one of the big manufacturers. So what made Matt decide to try his hand at bike building? "I figured that my dream EnduroCross bike didn't exist, so I just figured I'd build it myself. I really wanted something that was as light as a 250cc two-stroke, but without the 250cc hit that makes the bike sketchy on slick stuff, and with more power than a 125cc engine," Karlsen explains. "I figured that a KDX200 would be perfect, except the stock bike is about 250 lbs, really long and tall and the suspension is outdated. Since the stock KDX isn't anywhere near where I need it and nobody makes a modern day version of the bike, I decided to build my own."
The first step was to pick up a 2004 KXF250 with a recently exploded motor. "A buddy sold me the blown up KXF250 dirt cheap," recalls Matt, "So once I got that I stripped the trashed motor down and sold the cases, crank, radiators and some other parts on eBay-that's actually how I funded most of the project!" With cash in hand, Karlsen then purchased a '94 KDX200 engine (again on eBay) and completely rebuilt it using the leftover money from the four-stroke parts.
His next challenge was to mate the KDX motor with the 250F frame. Since the finished bike would be intended for EnduroCross applications only with no big jumps or landings, Matt chose to go with a stressed member frame, meaning that the engine is a supporting part of the frame. Karlsen spent several long nights in the garage measuring, cutting, welding and experimenting with the various components, and after some time was finally able to find a configuration that worked. Karlsen then recruited the help of his pal Larry Leavitt at LSE to finish some of the welds, and with that the bike was one giant step closer to being rideable. "One lifesaver is that I was able to mate up the carburetor in the original 250F air boot," says Karlsen of the process, "But the exhaust system was tricky. I got a new KDX pipe from FMF and went to work cutting and angling it to make it fit in the new frame. I had to cut, angle and weld a bunch of 45-degree angles to bring it back down underneath the shock reservoir like it should. It took some time but it finally lay in there nicely."
With the 200cc engine fresh and plugged into the new chassis, Karlsen turned his attention to the machine's intended purpose: EnduroCross. "The whole thing in building this bike was to try to make it bulletproof," Matt explains. "I didn't want to be able to fall over and break the radiator open or rip the water pump off, so I decided to put the radiator between the frame so there was absolutely no way to break it. I also took the water pump off, block-plated the stock one and put an electric pump underneath the radiator so that it circulates at all times. It took some time but I made the stock lighting coil power the water pump and a small fan on the radiator. I ran a small temp sensor on the cylinder to make sure it wasn't overheating."
In cradling the radiator between the frame spars, Karlsen effectively kicked the gas tank out of its stock spot. "I didn't have any place to put the gas tank, so out of necessity I built a two-quart fuel cell that sits underneath the seat and on top of the air filter. To do this, I took some sheet steel and hand built what I needed. It only holds two quarts, but that's plenty for an EnduroCross main event. To finish that part I took a Sawzall to the stock gas tank because I only needed the top half of it, so it looked like a normal bike." To complete the machine, Karlsen installed his trusty Flexx handlebars and Pro Moto Billet hand guards, as well as new graphics, tires and a little suspension work.
It all started with a road trip. Back in June of 2009, Journeyman racer Matt Karlsen was watching the scenery fly by on his drive home from the EnduroCross season opener in Las Vegas when he decided to build an off-road bike. Just like that. Whether this wild idea was created by Matt's tired brain just to keep him awake or not is up for debate, but either way the thought consumed Matt's brain for the duration of the drive. By the time he pulled into his driveway in Denver almost 12 hours later, Karlsen had a plan. He headed straight out to his shop and started tinkering, and four months later emerged with the bike of his dreams.
Now would be a good time to mention that Matt Karlsen is neither, by trade, a fabricator, nor is he a welder, engineer, architect or designer. Karlsen is a racer, and a pretty fast one at that. Be it at the Outdoor Nationals, EnduroCross, World Vet Championship or WORCS, it's not uncommon to see #940 roosting around the track in a respectable qualifying position. He's also an accomplished Triathlete, and has experience testing for one of the big manufacturers. So what made Matt decide to try his hand at bike building? "I figured that my dream EnduroCross bike didn't exist, so I just figured I'd build it myself. I really wanted something that was as light as a 250cc two-stroke, but without the 250cc hit that makes the bike sketchy on slick stuff, and with more power than a 125cc engine," Karlsen explains. "I figured that a KDX200 would be perfect, except the stock bike is about 250 lbs, really long and tall and the suspension is outdated. Since the stock KDX isn't anywhere near where I need it and nobody makes a modern day version of the bike, I decided to build my own."
The first step was to pick up a 2004 KXF250 with a recently exploded motor. "A buddy sold me the blown up KXF250 dirt cheap," recalls Matt, "So once I got that I stripped the trashed motor down and sold the cases, crank, radiators and some other parts on eBay-that's actually how I funded most of the project!" With cash in hand, Karlsen then purchased a '94 KDX200 engine (again on eBay) and completely rebuilt it using the leftover money from the four-stroke parts.
His next challenge was to mate the KDX motor with the 250F frame. Since the finished bike would be intended for EnduroCross applications only with no big jumps or landings, Matt chose to go with a stressed member frame, meaning that the engine is a supporting part of the frame. Karlsen spent several long nights in the garage measuring, cutting, welding and experimenting with the various components, and after some time was finally able to find a configuration that worked. Karlsen then recruited the help of his pal Larry Leavitt at LSE to finish some of the welds, and with that the bike was one giant step closer to being rideable. "One lifesaver is that I was able to mate up the carburetor in the original 250F air boot," says Karlsen of the process, "But the exhaust system was tricky. I got a new KDX pipe from FMF and went to work cutting and angling it to make it fit in the new frame. I had to cut, angle and weld a bunch of 45-degree angles to bring it back down underneath the shock reservoir like it should. It took some time but it finally lay in there nicely."
With the 200cc engine fresh and plugged into the new chassis, Karlsen turned his attention to the machine's intended purpose: EnduroCross. "The whole thing in building this bike was to try to make it bulletproof," Matt explains. "I didn't want to be able to fall over and break the radiator open or rip the water pump off, so I decided to put the radiator between the frame so there was absolutely no way to break it. I also took the water pump off, block-plated the stock one and put an electric pump underneath the radiator so that it circulates at all times. It took some time but I made the stock lighting coil power the water pump and a small fan on the radiator. I ran a small temp sensor on the cylinder to make sure it wasn't overheating."
In cradling the radiator between the frame spars, Karlsen effectively kicked the gas tank out of its stock spot. "I didn't have any place to put the gas tank, so out of necessity I built a two-quart fuel cell that sits underneath the seat and on top of the air filter. To do this, I took some sheet steel and hand built what I needed. It only holds two quarts, but that's plenty for an EnduroCross main event. To finish that part I took a Sawzall to the stock gas tank because I only needed the top half of it, so it looked like a normal bike." To complete the machine, Karlsen installed his trusty Flexx handlebars and Pro Moto Billet hand guards, as well as new graphics, tires and a little suspension work.