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By: Jason Giacchino
Email:
offthepegs@atvsource.com
July 2006
Fuel Injection 101
All the mags keep mentioning how awesome the
fuel injection is on the new Suzuki LTR450. If
it’s so great, why don’t all quads have it?
Trevor Murray
Trevor, that’s an excellent question that
deserves a good answer. To even begin to explain
the reasoning behind the praise bestowed upon
the modern fuel injection system we have to
first take a look at the technology it aims to
replace: The carburetor.
A carb flows fuel into the engine intake by
relying upon the vacuum produced by the piston
inside the cylinder. In other words, the faster
that piston rockets up and down, the more fuel
gets pulled down from the carb’s float bowl.
Once the piston is at rest, however, the
carburetor can no longer flow fuel and instead
becomes a miniaturized gas tank.
What then determines exactly how much gas
will become sucked into the engine with a carb?
Jetting; which are basically partially opened
ports that meter the flow of fuel.
 Fuel injection bypasses the entire float bowl
and finicky jets concept and even does away with
requiring a vacuum to draw fuel.
Rather, fuel is pressurized via an independent
pump (which usually runs off the battery) and is
then blasted directly into the engine through an
injector nozzle.
Since the fuel flow is no longer dependent
upon the piston’s activity, the CDI (ignition
computer) is now responsible for determining
precisely how much fuel should be injected in
direct relation to the situation at hand.
It is important to realize that fuel
injection doesn’t actually make any more power
than a well tuned carburetor setup. The real
advantage of fuel injection lies within
consistency. Carburetors are mechanical devices
and as such, there are situations where their
imperfection causes failure. An example would be
riding your quad through a sticky mud bog. Upon
nearing the shore you would likely wick the
throttle open for an instant boost of momentum
to free your machine from the slop.
Unfortunately, since the piston would be moving
slowly as you eased yourself though, so too
would there be little vacuum being created.
Suddenly opening the throttle results in more
area then the low vacuum pressure can swallow
and this is felt immediately as the engine bogs
down momentarily.
About the biggest disadvantage to the fuel
injection method of fuel flow is that it
requires the weight of a battery. ATV models
already lugging around a power cell for electric
starting duties have little to fear, but this
will certainly affect kick-start only, weight
conscientious, racers. The other, slightly less
significant disadvantage is that the only way to
tune a fuel injector is through electronics
(which will undoubtedly startle many backyard
mechanics). Mods to air boxes and aftermarket
pipes will require electronic ignition tweaking
whereas presently, simply swapping jets is all
that’s required.
Even with such disadvantages to consider, the
carburetor’s days are numbered. In answer to
your question as to why not all quads come with
fuel injection systems: It is still early.
Suberbikes have made the transition to fuel
injection as have nearly all automobiles. The
450R is simply one of the pioneers in bringing
the technology into our arena, an achievement
that will most certainly be followed by all of
the manufacturers in the near future. This is
especially true considering how favorably the
press has been reporting on the Zook’s
carburetor-less performance.
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