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KX500 KTM 350 XC-F Project Bike

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This article was originally published in the June 2017 issue of Dirt Rider.

Yes, that’s correct. Jonny Weisman of TBT Racing Arizona blended both motorcycles together for an incredibly beautiful piece of machinery. Jonny took an old 2002 KX500 engine that he had lying around and mounted it in a 2014 KTM 350 XC-F frame. Both bikes were unused in his shop, so he decided to create a 500cc two-stroke that implemented modern-day chassis and suspension technology, and the KX500/350 XC-F was born. Tons of labor went into Jonny’s project, as he was focused on making a clean, almost unmodified-looking machine. We had the pleasure of riding this unique beast at a local top-secret sand track in Southern California, and this is what we came away with.

First, let’s start with how Jonny got to this point and what he had to do to mate the Kawasaki engine to the KTM chassis.

More than 70 man-hours of labor were involved to create such a machine, as he had to bore the swingarm pivot hole in the cases to accept the KTM pivot bolt. He then cut out all of the original engine mounts, which actually all lined up pretty close but were just a tad too short. The head stay mounts, which are actually the stock KTM 350 XC-F mounts, were modified a little to fit. The intake boot was switched to a KTM 250 SX design and then was modified shorter to get the correct length. A Scalvini pipe took a lot of work to make fit, as it was designed for a Honda CR500AF; it came with no mounts because Jonny wanted to custom build his own mounts to fit properly with the Kawasaki engine and KTM mounting points. Clearing and angling the pipe to make room for the front tire, kickstarter, and cylinder water fitting were tricky and took some patience. The Scalvini silencer was also modified to get the correct angle to the pipe as well, and the radiators were fully welded to add strength and protect against leaks. The suspension is also unique, as the fork incorporates KYB inners and WP outer tubes, and finally the fork legs received the full treatment of Kashima coatings; the shock is a standard WP unit, valved for motocross use.

The minute we started the KX500 we knew we were in for a special treat. At first we had to retrain ourselves on how to start a 500 with correct procedure, but once we got it down the KX500 was easy to get fired up. Revving the engine is also a very foreign feeling to the arms. As much as the Fasst Co. Flexx bars helped with vibration, there was more than we could remember in quite some time. Once clicked into gear and the throttle opened, our smiles never seemed to diminish.

We were expecting a violent bottom-end hit, but instead we got a very friendly, tractable power delivery. Out of corners the KX500’s engine was smooth and predictable with great rear-wheel traction. This engine doesn’t have a real hit to it down low like a 450cc’d four-stroke, but instead it chugs along smoother and can be lugged as good, if not better, as any motocross four-stroke on the market today. Midrange power is where you’ll need to start holding on tight and gripping with your legs. Second and third gears are very usable with the big two-stroke. For a bigger-size engine the 500 can rev out fairly well. Case in point, we took a new Honda CRF450RX and the TBT Racing 500 two-stroke and drag raced them down a fire road and the 500 pulled the Honda slightly by the end of the half-mile. Only at the very end of the long straight was the KX500 able to start creeping away from the Honda four-stroke.

The chassis and suspension on the older Kawasaki 500s were decent in their day, but compared to today’s standards, they are subpar. Putting the Kawi’s engine in a KTM 350 XC-F chassis along with updated suspension really let us ride the mash-up to its full capabilities. Once out on the track and trails we immediately noticed how good the fork action was on the TBT Hybrid 500 two-stroke. The KYB internals from the SSS fork made the front end of the 500 feel more planted and didn’t have that mushy feeling the old set of Kawasaki forks would have had. Over small, rough, choppy sections of the track, the KYB fork offered a great feel and plenty of damping to keep the big two-stroke from pitching on decel.

We were skeptical of the WP rear shock and thought the mighty 500 would feel unbalanced on the track, but the rear felt comfortable on accel­eration and gave us a good amount of rear-wheel traction under load. We had to stiffen the shock a few clicks to prevent it from bottoming on G-outs, but overall the whole bike felt balanced and had a modern feel to it.

The chassis of the KTM 350 XC-F helps the 500 to corner a little better, but we weren’t carving inside lines like we would on a modern Honda or Suzuki. Its straight-line stability is better than its cornering capability, but for the area we tested at (very sandy with big bowl turns) it was a blast to twist the throttle on. Ergonomics were a lot better, as the seat-peg-handlebar ratio had a flatter feel and had us feeling like we were sitting on top of, versus inside of, the bike. For having a 15-year-old engine it’s amazing how easy it is to ride and how much fun you can have on a big-bore two-stroke. The newer KTM chassis helps this tremendously when riding a rough motocross track or when the trail gets hacked out. This was a very fun experience and let us reminisce and respect that much more all of the men who rode these beasts back in the day. All of us here at Dirt Rider love when a motorcycle enthusiast builds his or her own machine and it turns into a work of art. Jonny built this KX500/KTM 350 XC-F into a unique and one-off machine that was fun to look at. It was even more fun to twist the grip.