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Carb swap options with 4300A-equipped M-code '71 (351C)
#1
Hello fellows,

As I note that the 4300 doesn't particularly get rave reviews - not to mention that I've heard of a few fires starting due to a bad plug in front - I've been considering swapping to a Holley or Carter AFB.

That said, I have yet to pull the carb off the intake to verify what I have. Casting number on the intake is DOAE-9425-L, but that's a standard casting number for both the four and two barrel manifolds.

[Image: 71_mustang_12.jpg]

[Image: 71_mustang_13.jpg]

Nevertheless, if my research is correct, I should have a squarebore 4300A (P/N #D10FAAA) on a matching squarebore intake, which may or may not have a hot air passage on it (some places claim 1970-only; others say it was used in '71 as well).

That said, following are my questions:
  1. I've read something about the 4300's having a slightly different throttle plate size than similar carbs. I believe these comments are in reference to the spread-bore 4300D's, and does not apply to the 4300A. Am I correct in this assumption?
  2. If this thing has a hot air passage on it, do I have to fandangle any particular blockage plate or adapter to use a Holley or Carter AFB/Edelbrock?
  3. Which carb will require the least amount of adaptation to the factory linkages? It's a 351C with an automatic (has kickdown). I don't know yet whether I have a a C6, C4, or FMX hiding down there.

Advice appreciated.

Best,

-Kurt

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How to buy a '71-73 Mustang:
Rule #1: Assume all classic car sellers are guilty until proven innocent.
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#2
I had a squarebore 4300 on my 429. It had a hot air passage for the choke, but the tube internal to the engine and the tube running up to the choke were separate tubes (the "external" tube running up to the choke fit into the "internal" tube). With a little effort you can pull the external tube off the mounting plate without removing the plate, and if the internal tube is intact you will not have a vacuum leak. I swapped it with a squarebore Holley and it fit just fine. Look for a Holley with the Ford kickdown linkage. I had to grind a bit off the throttle linkage to miss the intake, but that bit I ground off was only used on Chryslers. NOTE: some carbs with the Ford kickdown will not work with AOD transmissions.

Steve



[Image: 25yvyp3.jpg]
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#3
sm3570;86548 Wrote:I had a squarebore 4300 on my 429. It had a hot air passage for the choke, but the tube internal to the engine and the tube running up to the choke were separate tubes (the "external" tube running up to the choke fit into the "internal" tube). With a little effort you can pull the external tube off the mounting plate without removing the plate, and if the internal tube is intact you will not have a vacuum leak. I swapped it with a squarebore Holley and it fit just fine. Look for a Holley with the Ford kickdown linkage. I had to grind a bit off the throttle linkage to miss the intake, but that bit I ground off was only used on Chryslers. NOTE: some carbs with the Ford kickdown will not work with AOD transmissions.

I'm not sure I explained it correctly - the car has an electric choke; not a hot-air choke. The "hot air passage" I'm referring to is the milled airway shown forward of the throttle bores in this picture:

(From: http://mustangtek.com/FordIntake.html)
[Image: D0AE-9425-L002_001.jpg]

It is also present on some of the 2V intakes.

EDIT: I think I just stumbled upon the answer - it's nothing but a heat passageway: http://www.stangnet.com/mustang-forums/t...ld.796922/ My mistake.

-Kurt

[Image: satellite-valiant-mustang-license-tags-signature.png]
How to buy a '71-73 Mustang:
Rule #1: Assume all classic car sellers are guilty until proven innocent.
Rule #2: No classic car dealer is ever innocent; thus, they are all guilty.
Rule #3: Buy from trustworthy people: Fellow forum members. Visit 7173Mustang's For Sale forum.
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#4
I think you need to plug it like the photo.
The manifold is stock 351C 4V and a Holley
with electric choke.

mike

   

[Image: 1_11_11_13_11_50_27.png]
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#5
The 4300A is not a perfect square bore. The primaries are slightly smaller than the secondaries. Not a pronounced difference like a 4300D. The intake is also not a perfect square bore. The intake can be made a true square bore easily with a die grinder if the intake is off the engine. The original choke would have been hot air heated. If the tube loop that is on the bottom of the plate shown in the picture is intact there won't be an exhaust leak (the loop sits in the exhaust crossover passage cast into the intake).
Everyone has their preferences on carburetors. For non-stock carbs I prefer Quick Fuel or Holley. The Quick Fuel carbs have more adjustability and that is helpful when tuning the carb to your specific application. Chuck
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#6
c9zx;86604 Wrote:The 4300A is not a perfect square bore. The primaries are slightly smaller than the secondaries. Not a pronounced difference like a 4300D. The intake is also not a perfect square bore. The intake can be made a true square bore easily with a die grinder if the intake is off the engine. The original choke would have been hot air heated. If the tube loop that is on the bottom of the plate shown in the picture is intact there won't be an exhaust leak (the loop sits in the exhaust crossover passage cast into the intake).
Everyone has their preferences on carburetors. For non-stock carbs I prefer Quick Fuel or Holley. The Quick Fuel carbs have more adjustability and that is helpful when tuning the carb to your specific application. Chuck

In short, putting anything but a 4300A on this intake will require that the intake come off for modification, correct?

If necessary, I can have tubing bent to match the position of the choke on a replacement carb; that's no problem.

-Kurt

[Image: satellite-valiant-mustang-license-tags-signature.png]
How to buy a '71-73 Mustang:
Rule #1: Assume all classic car sellers are guilty until proven innocent.
Rule #2: No classic car dealer is ever innocent; thus, they are all guilty.
Rule #3: Buy from trustworthy people: Fellow forum members. Visit 7173Mustang's For Sale forum.
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#7
If you are OK with leaving the primary holes as they are, a short (.250-.500) spacer plate/heat isolator that matches the bores of the new carb will allow the primary throttle plates to function properly and you won't need to remove the intake manifold. Something like this. http://www.holley.com/108-18.asp Chuck
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#8
Chuck - interesting! I put the Holley on my intake and manually operated the throttle and there seemed to be no problem with the function of the carb. The primary/secondary throttle plates aren't hitting the intake. Ran pretty good, just rich (but I'm now thinking that it's related to the ignition system). I haven't forgotten about your help troubleshooting my low vacuum issue but the car is still in the body shop.

Edit: Were all 4300 variations a not-quite-square bore? Because looking at cudak888's picture, I can see how the primaries are slightly smaller but I don't recall that on my 1970 429 engine.

Steve



[Image: 25yvyp3.jpg]
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#9
sm3570;86700 Wrote:Chuck - interesting! I put the Holley on my intake and manually operated the throttle and there seemed to be no problem with the function of the carb. The primary/secondary throttle plates aren't hitting the intake. Ran pretty good, just rich (but I'm now thinking that it's related to the ignition system). I haven't forgotten about your help troubleshooting my low vacuum issue but the car is still in the body shop.

Which intake do you have? Also a '71 M-code, I assume?

I'm guessing here, but it would sound as if the only logical explanation for what you describe is that the Holley plates are the same size (or smaller) than the smaller throttle bores on the stock intake.

sm3570;86700 Wrote:Edit: Were all 4300 variations a not-quite-square bore? Because looking at cudak888's picture, I can see how the primaries are slightly smaller but I don't recall that on my 1970 429 engine.

According to c9zx, that is correct - even the 4300A isn't a perfect square-bore, and the bores differ between the relative size. Here are two photos from eBay:

A. Seller doesn't ID this one except for a Delco rebuild tag. The slight difference between the secondaries and primaries can be seen in this photo. I'd say it's safe to assume this is a 600 CFM example with 1.25 venturis:

[Image: 30tmljm.jpg]

B. This next 4300 has noticeably smaller secondaries; seller claims this one is a '69 carb from a 351W, C9OF-D. According to the following .PDF article from the Mustang Times ( http://mustangtimes.net/33-11/pg48-50.pdf ), this is the 441 CFM variation, 1.00 venturies.

[Image: n18h7o.jpg]

Just to clarify sm3570's post, the Mustang Times article indicates that a 1970 429 would have come stock with the 4300A 600 CFM model - in which case, it would conceivably match example "A" above.

-Kurt

[Image: satellite-valiant-mustang-license-tags-signature.png]
How to buy a '71-73 Mustang:
Rule #1: Assume all classic car sellers are guilty until proven innocent.
Rule #2: No classic car dealer is ever innocent; thus, they are all guilty.
Rule #3: Buy from trustworthy people: Fellow forum members. Visit 7173Mustang's For Sale forum.
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#10
Unless you are going for originality, I would yard that boat anchor off, stash it in a corner, and drop an Edelbrock performer in it's place, with a 600 vac secondary holley.

1973 Mach 1 Q code 351 4V, 9A paint, standard interior, 3.50 rear, C6 trans.
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