PROJECT KTM 250XC-F
HUNTER THE 450
methodology for doing partial-throttle dyno runs. It turns
out that at a quarter throttle, a properly mapped motor can
often produce more power than at wide open, particularly
in the low-rpm ranges. After days of testing, it’s possible to
develop a very complicated map that has optimum spark
and fuel at each throttle opening. It takes longer to develop
an ignition map than it does to port a head or build a
The Vortex ignition allows you to select from 10 different
maps. You can switch between any two of these with a
handlebar switch. We had all 10 curves customized for different conditions. Nine of the settings were developed for
VP MR Pro- 6 race fuel; one was for pump gas. That last
one will become very important to us later, because we
like to ride a lot, and MR Pro 6 sells for $40 a gallon.
We finished off the motor with a Rekluse Core manual
clutch and CV4 radiator hoses for greater durability. As for
the rest of the bike, it was pretty much what you would
expect for an off-road KTM. The biggest issue, as we’ve
pointed out so many times, is the suspension. We went to
high-desert, crusty-old-guy Earl Schuler at ESR for that.
Over the years he’s been the go-to guy in desert racing for
riders like Ty Davis and Paul Krause. He has his own way
of approaching the WP4CS fork that involves rebuilding
the compression stack, opening up the cartridge and giv-
ing the fork a low-speed compression damping adjuster,
which it lacks in stock form. The shock isn’t redesigned
to the same degree, but frankly it doesn’t need as much.
What we like best about Earl is that he’ll work at the sus-
pension until we’re happy. Other suspension tuners just
argue with us about what we should like.
We used FasterUSA wheels with Dunlop MX52 tires and
a Sunstar sprocket. Cycra plastic, a TM Designs chain slid-
er and a TM Designs chainguide rounded out the package.
We kept the stock handguards, handlebar and gas tank.
One of the biggest problems with highly tuned
motors is the need for race fuel. We found a
way around that.