One-off: FMF doesn’t do engine work for customers anymore, but that doesn’t mean they’ve forgotten how. Every once in a
while, Donny Emler gets an itch he needs to scratch. Donny milled the head and reshaped the combustion chamber for a solid
MXA’s FMF/Fox Factory project had two simple goals:
(1) Fix the KTM 250SX’s weak link—the suspension.
Fox Factory, inventors of the most successful air shock in
motocross history, was up to the task. They took off the
stock WP rear shock and replaced it with a Fox Podium
RC3 rear shock, valved to Derek Howerton’s spec. The
shock used a 5. 4 kg/mm shock spring and featured all of
Fox Factory’s inventive technology, including their proprietary Bottom Out Control (BOC) clicker, Anti Wallow
Control (AWC) and FAST spring preload adjuster. As a
bonus, with the Fox FAST system, we didn’t have to deal
with KTM’s terrible nylon preload ring. The Fox Factory
RC3 shock retails for $995.
The WP forks also got the Fox treatment with new
valving, damping and tool-free, 35-click compression
adjuster caps. The forks used the stock KTM 0.44 kg/mm
springs. The fork valving retails for $225, and the
compression adjuster caps cost $199.
( 2) While Fox Factory worked on the suspension, FMF
took over the engine development program. The project
was quite unusual for FMF, because the only product
that they sell on the Derek Howerton replica is the FMF
exhaust system and silencer. The ported cylinder, milled
head, bored carburetor (from 36mm to 39mm) and jetting
were all handled by FMF, even though you can’t order
them from Uncle Donny.
In the beginning, we struggled with the setup of both
the suspension and the 39mm jetting. But, with basic
tuning techniques, we resolved every issue and got the
bike working like a dream. In back-to-back tests against
our stock KTM 250SX, there was no comparison. The
Dialing for dollars: The Fox Podium RC3 shock offered a lot of
adjustment compared to the OEM WP shock. The MXA test
crew went lighter on both low- and high-speed compression
damping than what Derek Howerton runs.