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FST Performance Carburetors;
248/779-8008; FSTcarb.comAn example of the ability to tune is this tight shot of an FST
metering block with the four emulsion holes. By changing the
size of one or more of the emulsion holes (arrows), a tuner
can make changes to the shape of the fuel curve.30 CAR CRAFT OCTOBER 2019
a small ECU that receives air/fuel
mixture feedback from a wideband
O 2 sensor located in the exhaust. This
electronic option will be offered on
complete carburetors or as an add-on
to an existing FST carburetor. FST tells
us this package is as yet not ready for
production, but should be on shelves
by the end of 2019.
But even without the feedback idea,
there are other FST tuning opportuni-
ties that might attract the more
sophisticated carb aficionado. Most
carburetors operate as a two-circuit,
fuel-delivery system. This refers to the
number of bleeds located at the top of
each venturi. A two-circuit carb uses
one air bleed for idle and the other for
main fuel delivery. FST offers options
that will include both three- and four-
circuit systems that can be quickly
identified by the number of bleed holes
at the top of each barrel. The three-
circuit concept first came into play
years ago on the Dominator-style race
carburetors, and FST has expanded this
option to a wider selection of sizes.
These additional circuits are mainly
used for additional midrange and
top-end tuning that cannot be accom-
plished merely by changing jets. These
are not really intended to be used onthe street, but intended more for appli-
cations like throttle-stop drag racing,
where the tuner can more accurately
create the ideal fuel curve throughout
the entire rpm band.
To create tuning opportunities with a
given carburetor, you used to purchase
custom parts and make the conversion
yourself. What FST has essentially
done is offer many of these options
now as standard equipment. It’s a little
bit like the car industry: What was
once considered a luxury option is
now standard fare. The best part?
The price is right for this new line, and
there are dozens of options; to dial in
exactly what you might need, visit the
FSTcarb.com website and poke around
with all of those available options.
When it comes to simple induction
options, it doesn’t get much cleaner or
simpler than a 750- or 850-cfm carbu-
retor on top of an aluminum intake
manifold. Now that tuning knowledge
is expanding, it’s more and more likely
that with a little bit of effort, you can
deliver near-EFI-like performance from
a fuel-metering device like a carburetor.
There’s still quite a future ahead for
these simple devices, especially if
you’re hip to making them work to
their full ability.On the large-by-huge flow side of things,
FST also has that area covered with monster
cfm capacity that ranges up to 1,450 cfm.
This 1,250-cfm Billet Excess carb has all the
cool options, including a billet-aluminum
fuel log. This happens to be a four-circuit
carb intended for the most serious of tuning
ventures.This view of the billet-aluminum float bowl
reveals the two small quick-change jet
hole slots that offer the ability to change
jets without removing the float bowl.
This requires the use of a jet holder tool
that captures the jet during removal and
installation.This Billet X-treme 750 carb shows the four
small idle bypass plugs. These bypass air
directly to the intake manifold. By drilling
or removing them, it’s possible to quickly
establish the proper idle speed without
disturbing the curb idle setting on the
primary throttle blades.The typical carburetor uses a two-circuit
bleed system, but FST offers an optional
three- (shown here) or four-circuit
possibility. In this three-circuit system, for
example, the third bleed adjusts midrange
fuel delivery.CARB MODEL LIST
CAST-BODY CARBURETORS
MODEL FLOW (CFM)
RT 600–750
RT Plus 600–750
RT X 600–850
RT X Viper 650–850
BILLET-BODY CARBURETORS
MODEL FLOW (CFM)
Billet X-treme 650–750
Billet X-treme Pro 750–1,050
Billet Excess 750–1,250
Billet Excess Pro 1,050–1,450