We ran a few of FST’s carburetors on
the dyno in a short tuning session
and were impressed with how easily
these carbs respond to even minor
tuning changes. FST’s Phil Freland
demonstrated just how quickly he
could make a significant change to
the entire fuel curve with a couple of
minor emulsion-hole changes.
them altogether, it’s possible to
customize the idle speed for
engines with very large cam-
shafts that idle at vacuum levels
below 10 inches of manifold
vacuum.
The tuning issue this addresses
is that big-cam engines require
much more throttle opening to
create a proper idle speed. This
requires a large primary throttle
blade opening that uncovers the
idle transfer slot. This delivers
additional idle fuel not metered
by the idle mixture screws, mak-
ing the engine run very rich and
less responsive to the idle mix-
ture adjustments. Bypassing air
using the FST bleeds allows the
tuner to close the throttle blade
position back to the proper posi-
tion with the idle transfer slot
barely uncovered. This allows far
more control over idle mixture
and eliminates the classic off-idle
stumble so common with big-
cam, carbureted engines. These
air-bypass fittings eliminate the
need to drill air-bypass holes in
the throttle blades, which was
previously the only way to
address this problem.
Four-corner idle is also available
on nearly every FST model (except
a couple of the entry-level RT
single-inlet carburetors), which is
also a plus for engines with bigger
camshafts that can benefit from a
more even idle mixture pattern in
the intake manifold. Another inter-
esting option available on many of
the FST carburetors is the RTX
Viper float bowl that creates a
center inlet for the billet fuel bowl.
At first, this seemed of minor con-
sequence until we attended last
year’s SEMA Show, where FST
introduced its electronic-feedback
system that incorporates an elec-
tronic solenoid at this center fuel
inlet. The solenoid is controlled by
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