JUST A LITTLE
We started off with a new Vertex piston. We went with
standard compression because we didn’t want to inhibit
high-rpm revs any more, which is a common problem with
increased compression pistons. Instead, we looked to the
cams. We installed Hot Cams Stage One cams for intake
and exhaust. We also went a little crazy with the pipe,
switching to the FMF Factory 4.1 RCT Ti full system with a
MegaBomb header. We removed the backfire screen from
the air filter cage, which is what all the cool kids do.
With the Yamaha Power Tuner, the possibilities for
remapping the EFI system are basically endless. It’s
impossible to know exactly what the differences are
between the motocross map on the YZ and the off-road
map on the FX, because the Power Tuner only references
the stock map. You adjust it by adding or subtracting
fuel at various rpm and throttle openings, but it doesn’t
allow you to install an entire YZ map—you just have
to experiment on your own. So, we went back to the
drawing board and tried a very different approach in this
department. For our current favorite settings, go to www.
dirtbikemagazine.com and search “YZ250FX Reboot.”
We had to consider the possibility that the FX was
making just as much horsepower as the YZ motocross
version, but the additional weight was what held it back.
The FX weighs 17 pounds more, and you can feel it in
most situations. Reducing the weight by that much just
isn’t practical, but you can save a pound or two. Switching
We have a season of racing on the Tusk wheels, Hinson
clutch and GPR stabilizer. All are holding up well.
250FX YZ The FX motor has a perfect power delivery, but a little more power wouldn’t hurt. We installed new cams and a new FMF Factory 4.1 Ti pipe and
remapped the ignition.
out the lead-acid battery for a lithium-ion cell saves over
2 pounds. Rocky Mountain ATV/MC has one that’s under
$100. The FMF pipe was worth another 2 pounds. We
figure if you pay less than $1000 for a pound of saved
weight, you’re ahead of the game.
In the time since our last report on our ongoing affair
with the YZ250FX, it has been used as a lab rat to test a
number of products. It has a set of Tusk wheels, which