Yamaha has a Mikuni fuel-injection system on the YFZ450. Keihin systems are
on many of the others. Of all the performance quads currently on the market,
only the Honda still has a carburetor.
you to toggle between setting one and
any other position that you preselect.
If you want to experiment with a map
of your own creation, there’s a setting
that can be tuned when hooked up to
MORE MOTORS, MORE MAPS
The Suzuki LTR450 has a slightly
different situation than the Yamaha. It
was sold as an EPA/CARB-compliant
vehicle, but Suzuki knew that racers
would embrace it. So at the factory,
the stock ECU was programmed with
an alternative map for fuel and spark
advance. This map was hidden, but
could be accessed by plugging a
resistor into the ignition, which was
sold by Yoshimura and called the
Cherry Bomb. That made government regulators very unhappy, but
it made the Suzuki the easiest EFI
machine to modify.
So for the Suzuki, is there any ben-
efit presented by replacing the whole
ignition? Absolutely. The LTR450’s
hidden map was another best guess.
Suzuki’s engineers anticipated only
mild modifications—a pipe and
maybe the removal of the stock air-
box lid. The Vortex X10 goes beyond
that, because its designers tested with
more combinations of engine mod-
ifications, intake and exhaust. Our
Suzuki was set up with a competition
exhaust and a K&N filter within a
less-restricted airbox; in other words,
minimal modifications. But even at
that level, the Vortex offered a perfor-
mance gain. The fuel mixture settings
were best at 5, 6 and 6 (low to high),
and the advance was set to position 7.
That gave the machine a universally
likable range of power.
Like most EFI machines, the Suzuki
is equipped with an air density sensor that is supposed to alter the fuel
mixture for altitude and temperature.
It does that fairly well, but if you ride
often at high altitude or in extreme
temperatures, you’ll need to be more
precise. Again, the Vortex allows you
to do your own testing and come up
with settings that are best for your
conditions. The same thing applies if
you run race fuel. Many blends are
oxygenated and require a richer mixture. The people who programmed
your ECU can’t possibly know what
you poured into the tank, and there’s
no sensor that can tell the motor how
to compensate. You have to be able to
make changes in the field.
As for the RZR, it’s the most complicated application of all for Vortex. The
stock Polaris ECU has more sensors
than any ATV because of safeguards
that are built in—things like brake-