THE MASH-UP MA­CHINE

Dirt Rider - - Route Sheet - Story By Kris Keefer • Photos By Pre­ston Jordan

We ride Franken­stein’s mon­ster to see if the mighty KX500 mo­tor mar­ries well with a mod­ern frame and sus­pen­sion.

DIR­TRIDER.COM THE BEAST

es, 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 mod­ern­day 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 topse­cret 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

Ya 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 rear­wheel 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 fourstroke 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 big­ger­size 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 twostroke from pitch­ing on de­cel.

We were skep­ti­cal of the WP rear shock and thought the

A 500cc

TWO-STROKE IN

FOUR-STROKE

CLOTH­ING

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 straight­line 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.

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Flexx Bars can only do so much to tame the KX500’S se­ri­ous vi­bra­tion. The Scalvini pipe is ac­tu­ally for a Honda CR500R and was heav­ily mod­i­fied to fit.

WANT MORE

Go to dir­trider.com/500-2stroke-hy­brid to check out the sights and sounds of the two-stroke hy­brid beast.

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