Zipper's Performance G/D Carbs - Manual (Page 2)

ThunderTech Products - 6655-A Amberton Drive - Elkridge, MD - 21075 - PH: (410)579-2929 - Fax: (410)579-2835
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unInG
I
nStructIonS
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ontInueD from
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ront
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aGe
Use of This Product is
Intended for Racing
Purposes Only.
VACUUM PETCOCKS
REMEMBER...
R
emembeR
:
T
uning
i
s
e
veRyThing
!
R
eplacement
p
aRts
& s
eRvices
MOUNTING
We recommend replacing
any late model vacuum petcock
with a Pingel High-Flow Petcock in
performance applications.
Check mixture after any Low
Speed jet change. At maximum rpm, all
three circuits are supplying fuel. If you
add fuel to one circuit, you may have to
take away from another as you have now
enriched the entire mixture throughout.
• ThunderJet kits and jets sizes
80-200
• Special S&S jets--air bleed jets
• Spacers and Insulator blocks
• Velocity stacks (racing only)
• High flow air filters
• Replacement parts and
mounting hardware
• Complete application-specific
carbs with ThunderJets
• Professional installation for
these parts
• Special application carbs
• Installation Fixtures
We have found there is a need
for enlarging the throat size in the Super
‘G’ Carb in certain big inch applications.
At mid-range rpm’s, air speed is simply
to high at the nozzle, resulting in a big
surge of fuel and its related stumble,
or sooty looking plugs. Lowering the
main jet size helps the problem but
dangerously leans out the mixture for
high rpm running (result-burnt pistons).
Boring the carb throat will lower the air
speed at the main discharge tube. This
smoothes out the fuel curve and allows
you to run adequate main jet sizes for
these big engines. If you choose to do
this modification yourself, be careful;
there is very little room for error here.
n
ote
: The suggested starting points are based at sea level. When looking at
the scale, consider that cam, compression, head flow and especially exhaust
type can greatly affect each circuit. Open exhaust systems such as drag pipes
will rely heavily on the ThunderJet circuit and less on the main jet for mid-range
to high RPM power; tune accordingly. Performance systems will generally tune
to the middle of the suggested jet range. Install baseline jetting and tune from
there. Refer to circuit instructions above for help with fine tuning specific RPM
ranges. Each engine has different requirements; time spent tuning will yield the
best results.
MANIFOLD SPACER BLOCKS
When tuning a long stroke
engine, increasing runner (manifold)
length may help control fuel stand-
off and improve low- and mid-range
carburetion. Different cams, exhausts,
strokes and other changes will affect this
area dramatically. If you are a serious
tuner, we suggest you purchase spacers
and insulator blocks and experiment with
them in your applications.
J
etting
R
ange
g
uide
F
oR
t
hundeR
J
et
t
uning
Tests on the Dyno and the track
have shown properly mounted carbs work
superior to units that move and shake due
to inadequate mounting. Make sure the
carb is properly and securely mounted.
DON’T OVERLOOK THIS AREA!
SUPER ‘G’ CARBS AND
TODAY’S LARGER ENGINES
UNDERJET