By: Jason Giacchino
June 2007 - Off The Pegs
While I typically devote my monthly column
space to musing and complaining, I’ve been
steadily compiling questions in desperate need
of answers. Without further delay let’s tear
into the mailbag.
"My friend and I have an ongoing argument that
I’m hoping you can help clarify once and for
all. In quad suspension what do the high- and
low-speed compression adjusters actually do? My
friend says they affect the quad’s handling at
high and low speeds, but I don’t think that’s
Any help in settling this matter is appreciated."
It appears you are correct in this friendly
argument. The high- and low-speed compression
settings do not refer to the speed of the quad
but rather the speed of the shock shaft in
response to the terrain it encounters. The
low-speed compression circuit is responsible for
suspension action in gradual elevation changes,
rolling mounds, and trail clutter while the
high-speed circuit kicks in during flat
landings, and when nailing square-edged bumps.
Typically you can identify the two different
adjustments on the shock by their appearance
alone. The low-speed adjuster generally requires
the blade of a screwdriver to turn while the
high speed circuit is usually tuned with a
special wrench. Remember that both of these
settings refer only to the shock’s compression
circuits and are entirely different from rebound
and preload adjustments.
"What’s the point of tunable end caps for an
Since the four-stroke has again taken over
the field, we are witnessing a flurry of new
technology to accompany the trend. Tunable
silencer caps are simply a very minuscule means
of adding horsepower to a quad at the risk of a
louder exhaust note. Conversely choosing a
smaller end cap restricts the quad’s ability to
expel spent vapor and robs it of power. The
benefit there is a quieter quad. The bottom line
though is that most pipe manufacturers perform
months of testing to produce a cap that finds
the happy medium between performance and sound.
They do this so that you don’t have to.
"I have a 2006 Yamaha YFZ 450 and love its
performance. Some of my riding buddies have
Suzuki’s and often brag that their fuel
injection gives them the edge over my carbureted
motor. Is there any truth to this and does a
bigger carb equal more horse?"
The first part of your question is very
simple: No, fuel injection makes no additional
power over a carbureted engine. The key
difference is that fuel injection makes the same
kind of power regardless of conditions whereas
carbs require jetting alterations to compensate
for any factors that affect fuel mixture
(elevation, engine mods, etc.). Fuel injection
relies on a computer and a fuel pump to deliver
the correct blend of gasoline and oxygen to the
motor while a carburetor is a mechanical device
that flows fuel and air on account of the
natural vacuum created as the piston travels
through its stroke.
A bigger carburetor does not necessarily mean
more horsepower. While a bigger carb has the
potential to move more fuel, the speed at which
the fuel travels into the motor is decreased.
This happens on account of the fact that it is
the piston speed that determines the rate of
vacuum drawing in the fuel. This means that
piston has to turn over quickly and steadily to
maintain a powerful enough vacuum to draw
sufficient fuel and air.
On the other hand, a smaller carb supplies less
fuel and air to the combustion chamber, but it
does so with a much higher velocity. So the
bottom line is that a bigger carburetor works
more efficiently as the rpms are flying (taking
away from crisp response down low) and a smaller
carb makes crisp low rpm response.
Like the answer to the last question, the
manufacturers spend lots of time and money in
testing to equip their models with a carburetor
that they feel delivers the most performance
across the power spread.