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Buy with confidence!
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return it within 30
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We ship world wide.
All international
orders must be paid
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Rebuilding a Quadrajet Carburetor
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No amount of effort spent on building a custom high-performance Quadrajet carburetor can be
successful unless we are working with a correctly rebuilt carburetor. Over the years I’ve come to
hate the word “rebuilt.” Most things I see that are “rebuilt,” especially carburetors, were probably
better off slam worn-out than after they were finished! This simply comes from lack of knowledge
rather than lack of skills. Armed with accurate and useable information, we can make sure that your
Quadrajet carburetor is correctly rebuilt, so it functions as it was originally intended. Working with a
unit that is up to par, we can go in and make metering and calibration changes to get the desired
and predicted results.
Most Quadrajets have experienced some wear through many years of use and countless heating-
up and cooling-down cycles in the engine compartment. This may leave some units in rather poor
overall condition. The decision to work on your current unit or select another core should be made
after careful disassembly and inspection of the castings. Before going into specific rebuilding
procedures we go over a few of the common problem areas. Once you have inspected the
carburetor and decided that it is in suitable condition to rebuild, you can continue on with
confidence that the final product works as expected.
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Here is a late-model
carburetor ready to go. All
parts have been plated,
bronze primary throttle
shaft bushings have been
installed, and the bottom
plugs have been sealed.
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Bottom Plugs
The design of the Quadrajet is excellent. There are no places for the main body to leak other than
the factory pressed-in bottom plugs. During the machining process it was necessary to access
several areas of the main casting from the bottom side. This mandated sealing them up afterwards.
On the bottom rear portion of the main casting there are two large pressed-in plugs. Very early
units have brass cup plugs.
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Very early carburetors
used pressed-in brass
cup plugs at the bottom
of the main casting. This
process was used
through 1968.
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The leakage rate for these units is almost 100 percent. Dabbing epoxy over them is similar to
cutting your arm off and putting a Band-Aid on it! Over time, the glue comes loose and the leakage
continues. A quick test to determine if the bottom plugs are leaking is to invert the casting and
apply a soap/water solution to the plugs. Using compressed air and a long tip on the air gun, apply
high-pressure air in through the main fuel-supply passages or pressed-in rear secondary disks.
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The most reliable test for leaking
bottom plugs: Apply a soap-and-water
mixture over the plugs, then introduce
high-pressure compressed air in
through the front and rear jet openings
in the fuel bowl. A small leak shows a
tiny stream of bubbles. Large leaks as
seen in this picture are easy to detect!
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If leakage is noted, the plugs are relatively easy to pull and re-install coated with epoxy or the
casting tapped for custom-made screw in plugs.
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The most reliable method to repair
leaking bottom plugs: Custom screw-in
plugs can be made from a piece of
threaded rod or the end of a bolt. Slot
the screw-in plug so it can be
tightened with a screwdriver. With the
threads coated, the epoxy is trapped in
place. Simply dabbing epoxy over the
leaking plugs does not work as a
long-term repair. The epoxy eventually
comes loose from the aluminum after
many heating-up and cooling-down
cycles of the engine.
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Later units made after about 1968 used pressed-in aluminum plugs. We still see a few of these that
leak, but not nearly as often as the early-style brass plugs. The method to install and swage in the
aluminum plugs continued to improve through the years of production. It is quite rare to find units
made from about 1975 and later that leak.
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The swaging process was
improved for later
carburetors. It is rare to find a
leaking bottom plug in the
1975 and newer units, but
they should always be tested
and repaired as needed.
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In addition to pressed-in rear plugs, several pressed-in lead plugs are found under the main
fuel-supply passages and one at a right angle to the accelerator pump checkball. It is rare for any
of these plugs to leak, but on occasion they do and must be removed and the casting tapped for
custom screw-in plugs coated with fuel-resistant epoxy.
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Once in a while a front plug shows
leakage. Again, the best repair is to
remove the old plugs and tap the
casting for a screw-in plug. The plugs
in the photo were made from hardened
#8-32 screws, shortened so they do
not extend too far into the casting and
interfere with fuel flow from the main
jets.
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Warped Main Body
Many castings show warping across the front. This is most often caused by over-tightening the long
front bolts. By design, the Quadrajet can withstand some warping across the front and still continue
to work fine. Once the center of the casting rises up and starts leaking, repair or replacement is
usually required.
Occasionally, we also see some warping on the bottom of the main body and air horn. The
Quadrajet uses a large, thick gasket between these parts. It is rare that the warping is severe
enough to cause vacuum leaks or any other issues once the carburetor is placed in service.
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Some air horns show warping across
the front. The Quadrajet can withstand
some warping and continue to work
fine. In some cases the center of the
air horn is raised up enough to cause
fuel to seep around the center of the
gasket. The air horn can be sanded or
machined flat to re-conform to the
main body.
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Stripped Fuel Filter Housing Threads
This problem is quite common on early models, mostly because of the age of the material and how
many times the fuel filter housing has been removed for filter replacement. There are several
methods that can be used to repair this problem; the most effective is the installation of a Heli-Coil.
The Heli-Coil gives the filter housing hardened steel threads to tighten into; it is a very good repair.
Several companies also market slightly oversized fittings with a self-tapping feature. They can be
effective for minor thread-wear issues, but the Heli-Coil repair is more effective and permanent.
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Previous | Next
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This has been a sample page from
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How to Rebuild and Modify
Rochester Quadrajet Carburetors
by Cliff Ruggles
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The Rochester Quadrajet carburetor was found perched atop the
engine of many classic GM and Ford performance vehicles. The
Q-Jet is a very capable, but often misunderstood carb. This book,
How to Rebuild and Modify Rochester Quadrajet Carburetors,
seeks to lift the veil of mystery surrounding the Q-Jet and show
owners how to tune and modify their carbs for maximum
performance. A complete guide to selecting, rebuilding, and
modifying the Q- Jet, aimed at both muscle car restorers and
racers. It includes a history of the Q-Jet, an explanation of how the
carb works, a guide to selecting and finding the right carb,
instructions on how to rebuild the carb, and extensive descriptions
of high-performance modifications that will help anyone with a
Q-Jet car crush the competition.
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Click below to view sample
pages from each chapter
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Chap. 1 - Quadrajet History
Chap. 2 - How Q-Jets Work
Chap. 3 - Carb Selection
Chap. 4 - Tools & Safety
Chap. 5 - Q-Jet Rebuilding
Chap. 6 - Performance Mods
Chap. 7 - Edelbrock Q-Jets
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"Unlike some tech books you've probably seen, this one does a
good job on the photography, with all color photos shot with good
lighting, clear details, and clean backgrounds." -Musclecar
Enthusiast, October 2006, reviewed by Steve Statham
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8-1/2 x 11"
Softbound
128 pages.
Approximately 300 color photos
Item: SA113
Price: $22.95
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Click here to buy now!
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This is a great book
anyone with a
Quadrajet will love!
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Holley Carburetor Handbook 4150 & 4160
In spite of the fact that the Holley 4150 and 4160
carburetors have been around seemingly forever, there
are still some people who are not well versed in the
tuning and rebuilding of these popular carburetors.
Whether you are a beginner or an experienced
enthusiast, with this book you can tune, repair, and
recondition a Holley carb for your vehicle like an expert.
Chapters also include the proper selection for your
application, how to tune for performance or economy,
and much more.
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Price:
$
13.95
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Rebuild and Modify Carter / Edelbrock Carburetors
How to Rebuild and Modify Carter/Edelbrock Carburetors
reflects the emergence of Edelbrock carburetors as the
predominant carburetors in the market today. Author David
Emanuel outlines carburetor types, gives a thorough look at
carb selection and carb function, and offers detailed
information on modifications, tuning, and rebuilding Carter and
Edelbrock carburetors. Also features the history of Carter as
well as the history of the AFB and the AVS since the purchase
by Edelbrock. Contains more than 300 color photos,
illustrations, and diagrams.
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Price:
$
22.95
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Super Tuning and Modifying Holley Carburetors
Super Tuning and Modifying Holley Carburetors shows you
how to select, install, tune, and modify all popular Holley
performance carburetors. This book gives a detailed view of
basic carburetor functioning, modifying for performance
applications, custom tuning for street, racing, off-road,
turbocharging, economy, and other special uses.
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Price:
$
18.95
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Payment, Shipping & Sales
Tax: Iowa
residents must pay 7% sales tax. Items usually ship
within one
business day of receipt of payment! Standard shipping is a flat rate of
$4.95 to
anywhere in the United States with USPS Media Mail.
Priority Mail shipping is available for an
additional $3.00, or
$7.95 for shipping. Shipping is combined and discounted for multiple item
purchases as follows: first item regular shipping price, add
$1.95 for each additional item. For
purchases of 3 or more items
shipping is automatically upgraded to Priority for no additional
charge! We offer world wide shipping and ship to Canada and Mexico
with USPS Priority Mail
International for $14.95, and to most
locations in Europe, Australia, Asia, Japan and South
America for
$18.95. Satisfaction is Guaranteed. Our store has a NO HASSLE RETURN
POLICY
within 30 days of purchase.
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