Bob's Resource Website (2007)

(Start date April 2001
Last update Jan 2007, Feb 2016)


    - Carter AFB 1 7/16" primaries, 1-1 1/16" secondries
      model 3506s
      Flow 637 (@2"Hg.) ( J. M. Long, Carter Service Rep -July 1968)
      Replacement = Carter CRT-9635 or Edelbrock 1406

      .089" (120-159) primary jets
      .077" (120-177) Secondary jets
      .058" & .069 (16-99) metering rods.

"I have a letter dated July 12, 1968 from Carter Carburetor Division which was in response to the question I asked about the carb CFM rating. Letter said; the 3506S Carter (R-1) has a rating of 637 CFM @ 2" mercury. Avanti, 1 (Anon 2004)


R2 Carbs
    Carter 3507s, 3588s, 3725s (pressure sealed) - 1-7/16" primaries, 1-11/16" secondaries
      Calibrated and sealed - Studebaker Part# 1561641

      flow 625 - 637 CFM (@2" hg)

    (Note:Carter #3507S,is an R2 Carburetor. It's the # that crossed to Stude#1560338

    (Aug 95 TW) Front jets 120-162 / .103
    (July 2005) Front jet is equivalent to a .101 Edelbrock. Rod is an odd size 76/45.
    ( I currently run my car with .101's and 75/47)
    16-263 is shown as the correct rod for carb#3507S, R2 Carburetor. That is the Carter # and crossed in my book to Stude#1560338. ( Erizzolo) Replacement Carter CRT-9635 or Edelbrock 1406 (Use Marine version or get kit to seal accelerator pump)

Aftermarket carbs have a larger air horn and will not allow the old R2 carb bonnet to be used. There are 2 fixes for this, either buy a new bonnet from Procharger at the cost of $150.00 or use this method by John Poulos:
  • " I finally grabbed an old AFB and tried the new style carb top gasket on it and it's the same ! I swapped all the new stuff over to the old top casting. Now I have modern AFB's bottom with the old style top that fits the bonnet correctly.
    I kept all the new stuff when I did the swap and I have the "strip kit if I need to rejet. BTW, I used an old AFB core off a GM car instead of a Avanti core. You may need to adapt the electric choke to work with the old top. With the carb I had, it just needed some bending to match up.
    I can tell you the top swapped fine, you even end up with the fuel line in the right place. I moved the floats and needle and seat to the old top. You may have have to mess with the choke linkage though. From what I can see the only difference in the new top is the neck and choke plate. It runs just fine, as I would expect it to, nothing in the fuel circuit has been changed, just had a new roof put on Just to be sure your carb is the same, compare the old and new gasket.
    My old top had a small vent hole just below the top center screw in the back, you need to plug it.

Sep 2006
After a couple of years tweaking the Edelbrock/AFB combination, it (the above) is rather simple but requires the venturi clusters to be changed and the air valve modified. All very simple stuff but performance and mileage improve drastically with these changes. Ernie R
R2 R5388

A "3725S" AFB carb is listed for "64V" R2's in the Jet Thrust parts book supplement. It's sometimes refered to as the "late R2 carb". A '63 R2 used 3588S. Avanti R2's used 3507S, 3588S (mine), or 3725S. The # is on a tag screwed to the top rear of the carb, (or lost!) ; and should also be stamped on the right front mounting ear.

A year or so ago, I researched jet and rod sizes for my 3588S; with an eye to leaning the primarys. These are notes I saved. If you have a 3724S, it's different. I'll look for stock sizes for it. There is some good information at, under "Tech Ref". There's also a chart of jet and rod sizes for the old style part #'s, in "Avanti Magazine" Fall/Winter 2003, issue 124.

The standard '64 Avanti R2 primary jets from Stude were .1015, with .076 X .049 rods.
First step lean R2 was the same jet with .077 X .0515 rods.
R2 secondary jets were .0935.
Standard R1 primary jets were .089, with .069 X .051 rods.
R1 secondary jets were .070, I think.

The original primary jets and rods, from Stude, were larger than are available now. You can subtract rod cross sectional areas from jet area; and find combinations of currently available jets and rods that give similar totals, richer, or leaner. A programmable calculator would save time. As far as I know, the new jets fit. The top of the rods may be different and require modification to the lever they hang from. Summit Racing has handy charts of available jets and rods, and their sizes.

Summit Jets

Metering Rods:
Summit Rods

For one step leaner than stock, on my R2, I figured EDL-1426, .095 jets; with EDL-1449, .070 X .037 rods.

For two steps leaner, same jets, with EDL-1455, .073 X .042 rods. Rods can be changed on the car, without removing the airhorn.

Five bowl/airhorn gaskets are EDL-1499.

Step up spring assortment is EDL-1464.

Marine accelerator pump, with seal for R2, is EDL- 1471; $22.69.

Inlet needle and seat, .110 size, is EDL-1466.

Mike M. (Jan 2007)

A little (more) information about the 3725S AFB.
Primary jets were .0995, (120-224). Rods were Carter #16-286; with 16-289 and 16-290U for one and two steps leaner. I can not find the actual sizes of these rods. Secondary jets were .0935, (120-166).
Mike M.

    -Carter AFB 1-7/16" primaries, 1-11/16" secondries
      Competition model Stude# 1558637
      Standard model 1563050
      model AFB-3808S
      flow 625 CFM (+-10)
      Primary jet # 120-159 Size (.089)
      Secondary Jet # 120-166 size (.0935)
      Primary metering rod # 16-103 size (.068 X .060)
      float setting 13/32"


    - Carter AFB 1-9/16" primaries, 1-11/16" secondries

      Front Carb
      Standard model Stude# 1563051
      flow 675 CFM (+-10)(est)
      Primary jet # 120-162 Size (0-1015)
      Secondary Jet # 120-176 size (.0635)
      Primary metering rod # 16-124 size (.069 X .0635)
      float setting 5/16"

      Rear Carb
      Standard model Stude# 1563051
      flow 675 CFM (+-10)(est)
      Primary jet # 120-162 Size (0-1015)
      Secondary Jet # 120-122 size (.070)
      Primary metering rod # 16-204 size (.073 X .063)
      float setting 5/16"

    they (R4 carbs) were Carter AFB's, 3810S for the front and 3811S for the rear. Based on venturi dia. and throttle bore size, the carbs are rated at 575cfm. Each. I've never been able to find any official Carter flow data for the Stude AFB's (or most any others for that matter). It's not even listed on the blueprints even.
    The Bonneville runs with the '64's were done in Sept.'63 and there were 12 cars there including 2 Champ 6 powered ones..
    There was only 1 R4 car built on the assy. line and it was the Daytona HT built for Car Life Magazine and featured in the article that was mentioned here recently. The R3 and R4 powered cars at the record runs were not built that way on the assy. line.

    R2Andy (SDC FOrum# 29620 - June 2009

    More R4 parts

    These pages and programming contained therin are © 1996 - , Bob Johnstone and may not be reproduced without the permission of rfjohnstone at (Bob Johnstone) All Rights Reserved.
    Some technical opinions are my own from experience, other informational data is from online sources with credits when available and while care has been taken to be as accurate as possible, it is offered only as a guide and caution should be exercised in the application of it.