Zipper's Performance G/D Carbs User Manual

Page 2

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ThunderTech Products - 6655-A Amberton Drive - Elkridge, MD - 21075 - PH: (410)579-2929 - Fax: (410)579-2835

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Use of This Product is

Intended for Racing

Purposes Only.

VACUUM PETCOCKS

REMEMBER...

R

emembeR

:

T

uning

i

s

e

veRyThing

!

R

eplacement

p

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& 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

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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

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