DID ROD BUSH GET IN TROUBLE WITH KTM
FOR FUNDING THE PROGRAM? No. Suddenly, thanks
to the crowd’s response to the sound of a 105-decibel four-stroke and the fact that we had proved that a four-stroke
could run with the two-strokes, KTM changed its business
plan and decided to start R&D on a race-ready production
four-stroke motocross bike. That bike came out in 2000
when KTM introduced the RFS engine.
DID DOUG HENRY’S VICTORY AT LAS VEGAS
ON THE YZ400 TAKE THE WIND OUT OF YOUR
SAILS? It depends how you look at it. I like to think
that Lance proved that not only could a four-stroke be
competitive, but that the fans in the stands appreciated
what we were trying to achieve. When Doug Henry won
in Vegas, it reaffirmed what we already knew. Yes, it
made the history of being the first to qualify moot, but
not the viability of the four-stroke.
TELL US ABOUT THE BIKE. WHAT’S INSIDE
THE ENGINE? It is a 1997 KTM 620 LC4 engine, but it
only shares the cases and the castings. I used a 620 crank
with a 400 piston to get 538cc. The transmission was a
three-speed. We kept second, third and fourth gears and
moved neutral between second and third. Lance could
never get the bike into neutral because we had ground
the detents to make it impossible for him to hit neutral on
the track. The pipe was made by FMF, and you will be
surprised to find out that it was made out of mild steel—
none of that fancy stainless steel or titanium back in 1997.
IS THAT A DELLORTO CARB? Yes, but not the
one that came stock on the 620. The 620 used a 40mm
round-slide Dellorto with a brass slide. I replaced it with a
38mm flat-slide Dellorto from a Husaberg. The 38mm flat-slide carb weighed less than the brass slide on the stock
carb. We hand-built a tapered velocity stack and tested it
Metal-Tek’s Chuck Warren
fabricated the aluminum tank
to fit the chassis and bodywork, but it fit a little too well.
The brake pedal was on the right, but the rear
rotor and caliper were on the left, which was
the European fashion back in the 1990s. It
required ingenuity to link it together.