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We ship world wide.
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Carburetor Tuning
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General Tuning Tips
I was once preparing to rebuild a carburetor, and in order to provide a proper environment in which
to perform the disassembly and reassembly, I was carefully cleaning a well-used workbench.
Puzzled by my sudden and uncharacteristic fervor for absolutely sanitary conditions, a bystander
who was observing the spectacle blessed me with a sample of his sarcastic wit. I simply responded,
“Cleanliness is next to Godliness,” to which he snarled, “Even in carburetors?” My reply, “Especially
in carburetors!”
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Dirt is to carburetors as
Professor Moriarty was to
Sherlock Holmes. A
good-quality high-capacity filter
should always be installed in
the fuel delivery system.
Low-restriction filters with
replaceable elements are
widely available.
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Too frequently, people who should know better lose sight of the fact that dirt and the always-
dreaded foreign matter can wreak havoc with an otherwise perfectly adequate fuel system. Racers
are especially vulnerable to dirt-induced problems since gas tanks from “recycled” cars are often
used, or a “custom” gas tank is made using improper materials or techniques. It seems strange that
a drag-race car driven 200 miles a year often experiences fuel system difficulties never
encountered with a street-driven vehicle that’s driven 100 times that many miles. To prevent
unnecessary dirt-provoked fuel problems:
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1.) Always run a filter of some sort, even if it just a simple inline element. For high-flow applications,
use a universal high-capacity filter with a replaceable element.
2.) Inspect the vehicle gas tank periodically to ensure that coatings or galvanizing have not begun
to come off.
3.) When using electric fuel pumps, inspect the pump periodically for accumulations of dirt and/or
rust.
4.) Flush all fuel lines before installation of new components or after rework.
5.) If you install a fuel-flow measuring device (as is usually included in an onboard gas mileage
computer), ensure that it is of sufficient flow capacity to accommodate full-throttle fuel requirements.
6.) When allowing a car to sit for extended periods of time, flush the tank and lines before refilling
the carburetor float bowls. Drain the gas tank and check for water in the fuel.
7.) Inspect electric fuel pumps for clogging or jamming when they are unused for extended periods
of time.
8.) If a vehicle isn’t driven regularly, add a can of “dry gas” at least twice a year to eliminate water,
which may ultimately cause fuel system corrosion.
9.) Inspect the air filter periodically and replace as necessary. A dirty filter reduces economy and
performance.
10.) Spray all air bleeds periodically with a carburetor cleaner—such as Gumout—to remove dirt
and fuel gum accumulations.
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A maze of plumbing was
Detroit's gift provided with every
new car delivered during the
early years of emissions
controls. These hose
menageries are inhabited by
vacuum leaks just waiting to
happen. Rubber hoses can
harden where they are
attached, crack, and leak air
without giving any visual signs.
A thorough inspection should
be a part of any restoration
effort.
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Heat
The dichotomy of carburetor operations is that fuel should be cool when in a liquid state but heat is
necessary for satisfactory vaporization. To this end, several techniques are commonly employed to
keep the carburetor as cool as possible, while heat is applied either to the intake manifold,
incoming air, or both.
For racing applications, it is common practice to block the heat riser passages in the intake
manifold or use a manifold and/or cylinder heads with no plenum-heat provision. The “cooling”
effect of this practice can improve horsepower by a few percent and is useful in competition where
every little bit helps. But for street-driven applications, the blocked heat riser can be of more harm
than benefit. The horsepower gain is still there to be had, but at the potential cost of fuel economy
and drivability. Without exhaust heat being applied to the manifold, fuel vaporization is inadequate
until the engine reaches normal operating temperature. In addition to minor drivability issues (which
are not really all that difficult to live with), excessive amounts of liquid fuel in the intake manifold can
reach the cylinder walls and wash away the oil that keeps rings and pistons happy. This may not be
a problem in a race engine where throttle movement is minimal when the engine is cold. But with the
“on-off-on” cycles that are required in traffic, or pulling away from stop signs or lights, the frequent
contribution of raw fuel squirted from the accelerator pump circuit can lead to rapid ring wear.
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In some vehicles, the incoming air is also pre-heated by the exhaust system. This is a further aid to
vaporization and enables an engine to run well on a leaner air/fuel mixture for emissions purposes.
The pre-heating systems are frequently discarded with no noticeable degradation in engine
operation. Some systems are designed to assist in meeting cold-start emissions requirements, and
as such have little positive effect on drivability.
Ideally, an engine should receive warm air when in cruise mode, and cold air when under full power.
A high-performance engine with a vacuum controlled cold air intake would operate under just such
an arrangement. In order to achieve optimum performance, it would be necessary to calibrate main
metering for the warm underhood air (leaner) and increase flow through the power enrichment
circuit (smaller diameter power step on the metering rods) to supply the fuel necessary for the cold
air at full power.
Along with whatever air supply system is used, it may be desirable to cool the carburetor to
minimize fuel percolation (fuel boiling in the float bowl resulting in stalling and poor hot-starting
characteristics) caused by high engine compartment temperatures. A thick insulating gasket
between the carb and manifold will help, but if percolation persists it may be necessary to install
ducts or diffusers to deliver a flow of cooler air past the carb exterior.
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Heat is both friend and foe to a
carburetor. A little is needed for
good vaporization, but too
much can lead to poor
performance, lean mixtures,
and percolation problems.
(Robert Genat)
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Cold
With all the plumbing that festoons emissions-era engine compartments, problems caused by
extreme cold are rare. However, when temperatures are between 30 and 50 degrees Fahrenheit
and humidity is high, carburetor icing can still occur during engine warm-up. Icing of an automotive
carburetor is almost always associated with low engine speeds (idle) where the gap between the
throttle plate and bore is minimal. Water vapor in the air condenses, freezes, and blocks the gap,
causing the engine to stall. Once normal operating temperature is attained, there is sufficient heat
at the plate/bore junction to prevent icing. With a properly functioning choke mechanism (with fast
idle provision) and the availability of manifold heat, icing should not be a problem.
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Fuel economy, and good
performance for that matter, is
only obtainable when air
restriction to the carburetor is
minimized. The highly
respected K&N cotton-wire
element air filter (right) will
usually outflow the standard
paper design. The K&N uses a
spray-on oil-based fluid that
permits cleaning and reuse.
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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
Carter/Edelbrock Carburetors
by Dave Emanuel
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If you want to modify your carburetor-equipped vehicle for
performance today, you can choose from three major carburetor
families – Holley, Demon, and Edelbrock. While Holley and Holley-
style carburetors like Demon have been popular for years with
their well documented successes and quirks, there has never
before been a book covering the ins and outs of the emerging
Edelbrock line of carburetors.
How to Rebuild and Modify Carter/Edelbrock Carburetors reflects
the emergence of Edelbrock carburetors as the predominant
Carter-style carburetors in the market today. A revision of the
best-selling title Super Tuning and Modifying Carter Carburetors,
this book contains more than 300 color photos, illustrations, and
diagrams, covering rebuilding, tuning, and modifying Carter and
Edelbrock carburetors.
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Click below to view
sample pages!
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1 - History of Carburetors
2 - Carburetor Types
3 - Selecting a Carburetor
4 - How a Carburetor Works
5 - Carburetor Modifications
6 - Carburetor Tuning
7 - Rebuilding Tips
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This book also features the history of Carter as well as the history
of the AFB and the AVS since the purchase by Edelbrock. 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/Edelbrock
carburetors.
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This is a great book
that anyone who
owns or works on
Carter or Edelbrock
Carburetors will love!
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8-1/2 x 11"
Softbound
136 pages
159 color and 156 b/w photos
Item # SA130
Price: $22.95
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Click here to buy now!
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Rebuild and Modify Quadrajet Carburetors
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. This is the only book to
truly cover step-by-step instruction on performance
building the Rochester Quadrajet!
A complete guide to
selecting, rebuilding, and modifying the Q- Jet, aimed at
both muscle car restorers and racers.
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Price:
$
22.95
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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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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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