Booster: The YZ250FX’s Yuasa battery weighs 4-1/2 pounds.
Worse yet, it forced Yamaha to raise the seat height.
Base material: For all intents and purposes, the YZ250FX
uses a YZ250F motocross engine, but there are compromises.
In the end, we carried 50-tooth, 51-tooth and 52-tooth
sprockets wherever we went. If we felt that the track
design favored good drive in second and third gears,
with less emphasis on fourth, we went with the 13/52
gearing. On tracks that were faster, had longer straights
and allowed the test riders to carry more speed through
the turns, we ran the broader and mellower 13/51 stock
gearing. It was, as with the KTM 300XC, always
Q: WHAT ABOUT THE MUFFLER?
A: The muffler that comes on the 2015 YZ250FX is
the OEM muffler that comes on European YZ250Fs. The
American muffler is a straight-through muffler without
any obstructions in the perf core. The Euro muffler has a
wing-like deflector in the core. In truth, we didn’t think
that the Euro-spec muffler was a big issue, but we took
the muffler from our YZ250F and put it on the YZ250FX
and were amazed by the performance gain. Obviously,
the consumer would be able to do just as well or better
by buying an aftermarket slip-on muffler.
Q: WHAT ABOUT THE ECU MAPPING?
A: Unlike on the WR250F, the FX’s black box is pro-
grammable with the $291.95 GYTR Power Tuner. Anyone
can reprogram his YZ250F, YZ450F or YZ250FX black
box in a few minutes with the Playstation-style Power
Tuner. All you do is punch numbers into the nine fuel
boxes (3-percent change per number) and nine ignition
boxes (1 degree per number) to get the setting you
want. We richened the fuel 6 percent in the midrange
and top end, and advanced the ignition 2 to 3 degrees
in every box (see the included map diagram). The new
map gave the YZ250FX more mid-to-top power. Throttle
response was crisper, and the bike was faster; however,
it traded some of the torquey feel of the stock map, and
we might be tempted to run the stock map in the woods
and the hopped-up map in motocross.
Q: WHAT ABOUT THE KICKSTAND?
A: As hardcore motocrossers, you’d think we would
eschew the use of a kickstand, but that thing was
sweet. We could come in from a ride, flip the stand
down and walk away. Of course, all motocross racing
organizations ban kickstands. Thus, we removed the
Q: WHAT DID WE DO WITH THE
A: Very little. We added 10cc of oil to each fork leg
to help hold them up longer in the middle of the stroke.
Apart from clicker settings, that’s all we did.
As for the shock, we had some issues—not with the
shock exactly, but with the rear of the FX chassis. The
first test rider who threw a leg over the YZ250FX had
his boot bounce off of the rear fender. He regrouped