|"Live wrong and Perspire"|
Anyone have opinions on the edelbrock carburetors? It's supposedly made by weber. A friend of mine swears by it. I recently acquired a 750 and am debating putting it on 5845
Aloha from Las Vegas,
I know a little about the smaller Weber-Edelbrock 500.
It's used here by the local Rover V8 specialist - claim it is more reliable and easier to tune than the the Holley 390 they used in the past and works well on 3.5, 3.9 and 4.6 litre motors.
They even use it as a replacement for the earlier Rover V8 injections systems.
If the 750 is similar it sounds like it could be a good reliable and flexible carb.
For info and pictures on the 500 (for comparison) see http://www.rpiv8.com/faq-carb.htm
Ex owner of #5012
> Anyone have opinions on the edelbrock carburetors? It's supposedly made by
> weber. A friend of mine swears by it. I recently acquired a 750 and am
> debating putting it on 5845
It's essentially a second generation Carter AFB. Weber (USA) manufactures
them and they are marketed in Europe as Webers. Holleys will make more
power and are better for dealing with cornering loads (when equipped with
center hung floats). The AFB's will be easier to tune for fuel economy
and be more reliable (no power valve to blow out, the only gasket is above
the fuel level so is less leak prone). Unfortunately the carb industry plays
fast and loose with testing standards. If you put a Holley 750, Demon 750,
and a Carter/Edelbrock AFB 750 on the same flow bench, you'll get different
flow ratings with the AFB flowing the least. A 750 CFM AFB does not flow as
well as a 750 Holley and will generally not make as much power but will be
easier to tune for fuel economy than a Holley. An 800 AFB/AVS (the AVS
version has an adjustable secondary, the AFB does not) is a better choice
for a modified 351C but a 750 AFB will be fine on mild 351C.
The Edelbrock AFB carb (not to be confused with their Rochester Quadrajet
clone) is a slight redesign of the second generation Carter AFB (Aluminum
Four Barrel). Edelbrock's version of the AFB is very similar to the Carter,
with the most notable difference being the use of "bottom feed" primary
boosters, with exits on the lower face of the delivery tube. Edelbrock
claims the bottom feed approach yields more uniform atomization relative
to the original Carter side feed boosters. The secondary boosters are the
same on both versions. Another difference is the Edelbrock accelerator pump
uses a rubber plunger instead of a one made of leather, as on the older
Carters. This may be better for vehicles that see long storage times
(doesn't dry out). The plunger is available separately and can be used on
the Carter AFB's. The Edelbrock AFB also has one less screw holding the top
onto the carb and they have switched to Torx fasteners in several places.
There are some other very minor differences in how the linkages are made.
Jets and 2-step metering rods are fully interchangeable between the two.
I'm not sure about the 3 step rods. Edelbrock's version of the AFB is
manufactured by Weber USA and sold in Europe under the Weber name. When
Edelbrock re-introduced the second generation AFB, Carter was no longer
producing it. Later, Carter (now owned by Federal-Mogul) re-introduced the
AFB under their own name. The ones I've seen are also made by Weber (and
say so on the main body) and may now be identical to the Edelbrocks (a
suspicion I have not verified).
If you choosethe AFB, Edelbrock has a nice owners manual that is available
It contains a step-by-step approach to tuning the AFB. Also of use would
be a copy of the carb section of a late 60's or early 70's Chrysler factory
manual. The Chrysler manuals cover the function and repair of the AFB
(also the AVS and ThermoQuad) in detail and have an excellent diagnosis and
trouble shooting section. Another excellent reference is "Super Tuning and
Modifying Carter Carburetors" by Dave Emmanuel, ISBN 0-931472-11-3.
When tuning an AFB, buy a strip kit (a collection of jets, rods, and step-up
springs) and possibly a set of squirters for your model.
AFB's use a different metering approach from Holleys and Autolites. Instead
of fixed primary jets and a power valve for enrichment, main fuel metering
in an AFB is controlled by a rod and jet arrangement. A tapered rod,
controlled by a vacuum-referenced, spring-loaded piston, moves up and down
in the jet to provide a variable area main metering orifice. This allows
the carb to adjust the air-to-fuel ratio for differing loads, as sensed by
the vacuum level. When the vehicle is cruising, the rod is on the lean step.
Under high load, low vacuum, conditions the rod moves to the rich step.
Carter AFB's may have two or three step rods, while Edelbrock versions are
all two step.
Secondary actuation also differs from the Holley approach. The secondary
butterflies on an AFB are opened mechanically in response to accelerator
pedal position. However, a counter-weighted flap, the air valve, is
positioned over the secondaries. The opening rate and amount the flap
opens is controlled by the airflow demand and the counter-weight (provides
the resistance the airflow must overcome). This arrangement was further
refined in the Thermoquad which used an adjustable (spring-loaded) shaped
flap to provide a variable venturi effect. Unfortunately, the counter-
weighted air door on the AFB is not easily adjustable. It can be quickened
by removing weight (with a grinder) or slowed by making it heavier. The
AVS version (originally a Carter design is now available from Edelbrock)
is nearly identical to the AFB but has an easily adjustable spring-loaded
The idle adjustment screws are on the font of the carburator which puts
facing the rear window on a Pantera. You can use a stubby screwdriver if
you have the reach or one of the flexible carb tuning screwdrivers with
the gripper ends. The Holley is nicer in that reguard. One other area where
the Holley is better is the float adjustment. On an AFB, you have to take
the top off (no big deal) and bend the float tangs. On a Holley, you can
adjust the floats externally.
AFB's like Holleys also have replaceable primary shooters. AFB's do have
mechanical linkage secondaries but they operate more like a vacuum secondary
carbs and do not require a secondary side accelerator pump due to the use of
the air door that restricts secondary airflow until the demand is high
enough to pull fuel through the jet without a bog.
The step-up springs and second step on the rods serve the same function
as the Holley power valve and power valve channel restrictors and are
much easier to change. On an AFB, the rods and springs are accessable
from the top cover. On a Holley, you must disassemble the carb to get
at the power valve and the PVCR's are fixed orifices which must either
be drilled out or epoxied shut and re-drilled.
Holleys have the choice of center or side hung floats. AFB/AVS all are
side hung. If you plan on hard cornering, you'll want center hung floats
since they are
much less susceptible to cornering loads and fuel slosh. Side hung floats
have a pivot at one side of the bowl (the pivot pin runs front-to-back in
the carb) and a long float that extends to the other side. With that
arrangement, mechanical leverage is significant and a slight slosh at the
far tip can cause the entire float to move. With center pivot floats, the
pivot pin runs side-to-side and the mechanical leverage is much lower, so
slosh in the corners doesn't lift or drop the floats as easily. You can
change from side hung to center hung floats by simply by changing bowl and
float assemblies. If you don't know which style float your carb is equipped
with and don't want to remove and inspect, the Holley catalog lists the
float style for each carb part number. There are also road race floats with
reduced volume at the edges. They don't bounce around as much due to slosh
(the slosh climbs the wall of the bowl). Those are fairly popular among the
serious road race crowd, but not mandatory for most track cars. Holley also
makes jet extension tubes that makes the jets less likely from being
uncovered during hard accelerations. While these may be necessary in some
extreme cases, in many cases it's the floats. With center hung floats and
the proper float level, the extension tubes, road race floats, etc. aren't
usually necessary. Note that that the float level must be properly tuned
for your configuration. It's usually at the edge of the inspection hole
but not always, particularly on Panteras with non-level intake manifolds.
Trial and error with hard acceleration, cornering, and braking runs is the
only way to know for sure. For drag racing, the side pivot floats are
While the AFB/AVS floats are mounted on the side, the pivot is arranged like
a center-hung Holley, so the Carter should be relatively insensitive to
cornering-induced fuel slosh (and relatively more sensitive to braking
and drag launches). The float level can affect this behaviour but if
that's set properly, it's still possible to drain the bowls during long
sweeping corners. I'd guess the AFB/AVS carbs are not as good as center hung
Holleys in the corners buit better than side hung Holleys.
On an AFB, one bowl per side feeds that side's jets (one needle and seat
per side). High performance applications often require a higher flow needle
and seat assembly which are available.
The accelerator pump stroke is adjusted externally via a three-position rod
and clip arrangement. The stroke controls the flow volume but not its
duration. To adjust the duration of the flow, the squirter nozzle size must
be changed (a smaller nozzle hole takes longer to discharge a given volume
of fuel). Several shooter sizes are available but may be too small for some
engines. The shooters can be drilled out but be sure to leave enough wall
thickness on the tubes so they won't crack over time. A number series drill
bit of suitable size and a pin vise work well for enlarging the nozzles.
Opening the throttle compresses a spring which applies pressure to the
accelerator pump piston which drives fuel through the shooters. The total
volume of fuel furnished is a function of how much the throttle is opened
and is somewhat nonlinear because of the geometry of the linkage. The
linkage can be bent for fine tuning.
AFB's are more sensitive to fuel pressure and float level. At idle, there
should not be any more than 6.0 psi; if the vehicle has an adjustable
fuel-pressure regulator, set it to 5.5 psi. The carb may perform well with
higher presure, but will be prone to stalls on quick turns and stops with
the clutch disengaged. Minimum fuel pressure (at high RPM and WOT) should
not drop below 2.0 psi. If it does, a fuel pump with more capacity is
The step-up springs are color-coded instead of rated by vacuum level like
a Holley power valve. I can't recall if the Edelbrock manual correlates
this but if it does, you can set the enrichment just as you would a power
Once you realize the spring acts like the power valve and the second
step on the rod acts like a Holley PVCR, you can tune them pretty much
like a Holley.
In "How to Make Horsepower - Volume 2: Carburetors and Intake Manifolds",
Vizard had this to say about the AFB: "So how well do the Carter clones work?
The writer's limited experience here has shown positive results, but talking to
people within the performance industry, it appears that this carbs greatest
fans are among those who run chassis dynos for a living. The comment, so often
heard, is that the carb can be calibrated to hold very precise air/fuel ratios
over the entire working range. This results in good mileage, driveability and
power with no apparent compromises."
However, I know of a couple of guys who have attempted to tune AFB's on
chassis dynos and found little change in WOT air-fuel ratio no matter what
rods/jets the installed. They only affected AFR at at part throttle.
My guess is the needle and seat wasn't passing sufficient fuel. The AFB
uses the rods, jets and step up springs only on the primary side. They
primarily affect part throttle. The secondary side is jets only so jetting
up the secondaries should make a difference at WOT. When it doesn't, it's
likely due to the needle and seat. On an AFB, one bowl per side feeds that
side's jets. One needle and seat per side. High performance applications
often require a higher flow needle and seat assembly (which are available).
If the needle and seat limits the flow, increasing the jets won't make much
|"Live wrong and Perspire"|
I guess that since there are no definite negatives, I guess that I can try running it and see. I'm not going for HP, a mild reliable motor is what I'm after.
Dan as usual, you're a wealth of knowledge. Thanks for all your time and assistance! BTW, can you contact me either email or phone (808) 782-1545 Thanks
Aloha from Las Vegas,
I just sent you an email.
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