cage, which, according to Dave, is no easy feat since the
stock cage and reeds are very good. The Moto Tassinari cage
makes more bottom, peak and over-rev.
For the exhaust system, they tested both the FMF Fatty and
the FMF Gnarly pipes. The Fatty pipe’s power is different from
the Gnarly in that it’s broader, more seamless and carries further into the rpm range. The new Fatty uses a running change
that David Vuillemin tested when he was a factory Yamaha
rider, and this focused on a strong middle and top. The Gnarly
is thicker and offers a more abrupt hit that targets off-road,
and then lacks the good over-rev needed for moto. It comes
down to personal preference. In the faster terrain of the west,
top is good. Back east, a rider might want the extra grunt.
Considerable effort went into the jetting specs, which
work well from sea level to 4000 feet. They are a 48 pilot,
an N3EW needle with the clip in the number two position, a
178 main and the airscrew set at 1 3⁄ 4 turns out. Use a 175
main for 4000–6000 feet of elevation and a 172 for
6000–8000 feet. Temperature is also a factor; these specs
work for temperatures between 70–90 degrees. Also, do
not disconnect the TPS sensor or power jet on the carb.
They both increase power when they are working properly.
According to Dave, the power jet in the Keihin carburetor is
a funny thing. It actually adds a whole horsepower to the
over-rev when it’s working, but you lose that horsepower if
you disconnect it or run oil that is too thick. Using synthetic
Silkolene at 40:1 made one more horsepower on overrev
than bean oil did at 50:1. The bean oil was just too thick to
flow through the small power jet orifice, causing the same
horsepower loss as disconnecting it.
Lastly, quiet power is crucial, and the FMF Q Stealth system actually makes more power than one would think for a
system targeting sound. Quietness is usually associated
with less power, but according to BDSB and the dyno
results, this clearly isn’t the case with the Q Stealth. BDSB
says, “Thank you, FMF, for the Q Stealth.”
SUSPENSION & HANDLING
Over the years Yamaha has had great results with the KYB
SSS fork. It works really well on a motocross track, but if
you’re like most of us, you probably don’t spend 100 percent
of your time at the track; instead, you typically head out to
the trails on the weekends to dice it up with friends. Off-road,
you’ll quickly notice that motocross suspension is designed
for motocross. While backing all the way out on the compres-
sion and playing with the rebound a bit will reduce some of
the deflection and kicking, the bike will still wallow in the rear
and deflect on square-edged rocks and roots.
Dave enlisted Moto Lab, a suspension company out of
Arizona, to rework the YZ’s components. BDSB has a long
history with Moto Lab and has high praise for Moto Lab’s
ability to modify motocross suspension for off-road.
According to Moto Lab, “Suspension is always a compro-
mise. You can’t have 100 percent suspension bliss in gnarly
rocks and then head back to the track and not expect to bot-
tom out over big jumps.” So knowing that the machine was
all about off-road, Moto Lab was able to come up with a bal-
anced suspension package that was plush but firm initially
and didn’t blow through its stroke on hard landings.
The guys at Moto Lab stripped down the fork until every
last shim, bushing and spring was out, and then they put
together the base valve using the stock KYB piston and
stacked it on top of a pressure spring chosen for the target
175-pound, experienced rider. The stock pressure springs,
which affect mid-stroke harshness and chop over square-edge bumps that are rated stock for a 280-pound rider,
were reset for the intended buck seventy-five weight. Next
were the mid-valve mods, which help to blend the valving
AUGUST 2013 / DIRT BIKE 47
Smooth power feels docile, although it makes almost 4 more
horsepower than stock. It hooks up and loves the tight stuff.
Moto Lab dissects the suspension, and
then valved it for a plusher, more off-road-oriented ride.
Fitting on the wider and grippier Torq 1
footpeg with the replaceable teeth was a
big plus, and so was the Torq 1 brake
pedal with the adjustable tip for toe-kick
mobility. Good stuff!
The stock Pro Taper bars were used;
they were complemented by Fastway’s
steering damper and handguard system. The unit has superb adjustability,
and the mounting system is trick.