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Old 05-11-2008, 03:53 PM
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Default Autolite 4100-4300 Carb Info

Here is some info that might be helpful that I stumbled on a few minutes ago...

Is the Ford 4300D stock spreadbore carb an Autolite or Motorcraft carb?

It's a Motorcraft 4300D. The Autolite 4100 was an earlier design and
was replaced by the 4300 and 4300D in most of Ford's OEM applications.

Or, are they all the same carb? Same carb used on the Boss 351s?

4100 and 4300 are completely different designs. Some info on each is
listed below. The Boss 351 used a 4300D with jetting and power valve
trip point matched to the Boss cam.

Dan Jones

Ford replaced the Autolite 4100 with the Motorcraft 4300 and a spreadbore
version, the 4300D. Most 4V Clevelands were fitted with one of the Motorcraft
units. Both the 4300 and 4300D use air valve secondaries with fixed jets and
power valve enrichment. The 4300D has the standard Holley/Autolite bolt
pattern which is unusual for a spreadbore and means they will not directly
mount up to most spreadbore manifolds, other than factory Ford intakes. The
only aftermarket intake manifolds that I'm aware of that will directly mount a
spreadbore 4300D are the Holley Street Dominators and Strip Dominators. Those
intakes have a trapezoidal plenum opening that clears the large secondary
butterflies. However, other intakes can be made to work using an adapter

Model CFM Venturi Diameter Bore Diameter
primary secondary primary secondary

4300 441 1 ?? 1 7/16 1 9/16 67-68 302 J-Code
4300 470 1 ?? 1 7/16 1 9/16 69 351W
4300 595 1 1/4 ?? 1 9/16 1 11/16 69 390 S-Code
4300 600 1 1/4 ?? 1 9/16 1 11/16 70 351W, 351C
4300 605 1 1/4 ?? 1 9/16 1 11/16 71 351C
4300D 715 1 1/4 ?? 1 9/16 2 71 Boss 351C, 72-74 351C

4300's have a reputation of developing leaks at the front of the carburetor
between the lid or air horn, and the main body. If you plan on modifying your
engine, remember the selection of power valves is very limited so it will be
difficult to tune properly. Also, there are no books on the market for
modifying or performance tuning the Motorcraft carbs. Your best source of
information is a Ford factory repair manual. Jack DeRyke thinks they are an
instrument of the Devil :-)

Dave Doddek reports he spoke with someone who says that AMC made a special
float for the 4300 Motorcraft carb that changed the pivot some how and would
eliminate the cutout problem during cornering.

Only the early model 4300's have adjustable secondary air valve. The
adjustment procedure is:

1. Loosen clamp screw and let housing rotate to no load position.
2. Hold air valve in closed position.
3. Scribe reference mark.
4. Rotate nylon spring housing counter-clockwise the proper number of knobs and
then tighten screw.
5. For 1967-1968 applications the proper number of knobs are:

289 manual 5 knobs
289 auto 4 knobs
390 7 knobs
410-428 8 knobs

Autolite 4100

Probably the simplest of the modern 4 barrel designs (only about 30 parts), the
Autolite 4100 was installed on a variety of Ford V8's. The metering approach
is similar to a Holley with fixed jets, power valve enrichment, and
conventional vacuum secondaries. Annular boosters and a one piece main body
casting are used. Owing to its simplicity and one piece body, the 4100 has a
good reputation for reliability. The Holley 4010 carb is basically a re-design
of the Autolite 4100.

Pony Carburetors also markets what they call a "spreadbore" version of the 4100
by combining a 1.00" primary venturi diameter with a 1.18" secondary. Note
that this carb is only slightly spreadbore (like many AFB's) and will bolt up
to normal squarebore intakes. One word of warning about the 4100's, they are
prone to vacuum leaks at the carb base when mounted on some aftermarket
manifolds which have thinner than stock mounting flanges. Holley 4010's and
4011's also have this reputation.

Model CFM Venturi Diameter Bore Diameter
primary secondary primary secondary

4100 441 1 ??? 1 7/16 1 9/16
4100 480 1.08 ??? 1 7/16 1 7/16 64-66 289 A&D-code
4100 480 1.08 ??? 1 7/16 1 9/16
4100 600 1.12 ??? 1 9/16 1 9/16 289 Hi-Po
4100 ??? 1.19 ??? 1 9/16? 1 9/16 1958 only
4100 ??? 1.00 ??? 1 3/16 ??? Pony Carb spreadbore

Question - Do all the 4100's have the same size primary and secondary venturis,
also check to see if Holley jets, power valves, and vacuum diaphragms

Data from Bob Sprowl

I took five Autolite 4100s to a local speed shop. One 4100 had the small 1.08
primary venturi and the rest had the larger 1.12 primary venturi. The small
one flowed 441 CFM, the larger ones flowed 503 to 528, averaging 520. These
results were very close to what I expected for the 1.08 but 50 CFM higher for
the 1.12. Still the 1.12 does not flow 600 CFM as claimed by some vendors.

The testing was done at Charlie's Automotive in Apex, NC. They are an engine
builder for the local NASCAR guys. The tests were done on a Superflow 1020
flow bench which is computerized and automatically corrects the output data to
standard temperature and pressure. The flow testing was done at the SAE
standard for 4 BBL carburetors - 1.5 inches of mercury, which is the same
standard used by Holley, Edelbrock and Carter.

Type or No. , _ Primary, _ Primary, _ Scndry, _ Scndry ,_ CFM test
Tag or ID ____ Venturi, _,_ Bore _,_ Venturi,_ Bore, _,_ Results
C6AF-E ______ 1.08 ____ 1.437 ___ 1.18 ___ 1.437 ___ 441
EDT 84D _____ 1.12 ____ 1.562 ___ 1.18 ___ 1.562 ___ 503
EDT-17BR ____ 1.12 ____ 1.562 ___ 1.18 ___ 1.562 ___ 523
C4SF-B ______ 1.12 ____ 1.562 ___ 1.18 ___ 1.562 ___ 526
C4AF-DG, ____ 1.12 ____ 1.562 ___ 1.18 ___ 1.562 ___ 528

Additional information from Eric Riggert (

I looked up all the Autolite 4100's listed in my '66 Ford manual, and here they

Application: P/N Primary P. Jet S. Jet Power Valve
289-4V Std. C6ZF-A 1.08 49F 58F Plain
289-4V Std., Therm. C6ZF-D 1.08 47F 58F Plain
289-4V Std., HiPo C6ZF-C 1.125 52F 68F Plain
289-4V C-4 C6ZF-B 1.08 48F 57F Plain
289-4V C-4, Therm. C6ZF-E 1.08 46F 58F Plain
390-4V Std. C6OF-D 1.08 49F 67F Plain
390-4V Std., Therm. C6OF-H 1.08 48F 46F* Plain
390-4V C-4 C6OF-E 1.08 48F 67F Plain
390-4V C-4, Therm. C6OF-J 1.08 47F 67F Plain


* I don't know if this is a typo or if the 46F secondary metering jet is
used in the 390-4V smogged engine for emissions reasons. Anyone?

1. Power valves for all carbs are listed as 'Plain' for normal use, and
'Green' (in color) for high altitude use. Presumably the green power valves
give a different (leaner?) mixture to make up for the thinner air (less oxygen
in it).

2. Jet sizes change slightly for all applications. In addition, choke
plate settings, idle speed settings, accelerator pump linkage settings, etc.
change slightly for each carb. However, it seems that the main casting is the
same for all 4100's (except for primary venturi size), so it would seems that
any 4100 could be adjusted to any other 4100's specs. (Pony Carbs can and will
do this as requested when they rebuild your carb - just tell them what engine
the carb is going on and you can discuss all sorts of possibilities).

3. In '66, the only carb to get the larger venturies (at least in the
Mustang/Falcon/Fairlane manual) is the 289-4V HiPo -- the 'K' engine.4. The
venturi diameter (1.08 or 1.125 inches) is cast into the side of the carb. --
just look on the driver's side of the front float bowl.

Ray Clark - Squarebirds Administrator
'59 Tbird "The Yellow Rose Of Texas" aka "Tweety Bird"
"It's Hip To Be Square"
Thunderbird Registry #33025 VTCI #11178

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