AFB Jet Sizes/Numbering?

Discussion in 'Carter' started by wildcat2, Jul 7, 2005.

  1. wildcat2

    wildcat2 Well-Known Member

    Who knows how to figure out AFB primary and secondary jet sizes from the numbers? In the Dave Emanuel Carter Carb book it says jets are numbered 120-xxx, with 120-3xx being sizes under 0.100 and 120-4xx being 0.100 and over. There's no mention of 120-1xx and 120-2xx, which are the sizes listed in the Service Manual.

    I bought a "rebuilt" '65 front 2x4 carb (3645 SB) off Ebay a few months ago and am just getting around to going through it. While the carb looks very pretty, there were NO secondary jets installed. The factory manual calls for 120-222 secondary jets on both front and rear 2x4 carbs. The single carb 425 has 120-159 jets.

    Would the 2x4 carbs have been jetted 0.063 bigger than the single carb? That doesn't seem right. Can anyone explain the numbering used on the factory jets? And where is the best place to get 120-222 (or equivalent) jets?

    I am piece-mealing a 2x4 set up for my stock '65 401. I am using a single 4 barrel carb (3921 S) for the rear and fabricating a factory appearing progressive linkage. Any recommendations for an initial starting point on jetting would be appreciated.

  2. Buford

    Buford Old guy member

    Sorry for the late reply. I finally found my Carter literature. Until about the 1970s, Carter's jet and metering rod numbering system was a real "dog's breakfast" where the 120-1xx or 120-2xx number was not the jet size, just a part number. At some time "the light came on", and the part numbers (most) became 120-(jet size +300). A .098 jet became 120-398. The metering rod numbers also became the actual sizes. A rod with .072 and .055 diameters became a 16-7255.Someone deserved a bonus for some common sense; but Carter continued to use a few of the old numbers for a few sizes...??? The Buick service manuals for the '60s used the old system for jet identification. The 120-222 jet you mentioned is actually .070 diameter according to the Carter size chart. Edelbrock uses the same jets, but their part numbers are their own system, and I believe the smallest they have is .077 (EDE1420). This seems small (lean) to me. VERY CONFUSING!!! I need a beer!:) Frank
    P.S. Let me know if I can be of further help. I have a 1964 Buick service manual (big car) that lists jet/rod sizes for the Carters, and my Carter books.
  3. wildcat2

    wildcat2 Well-Known Member

    THANKS Frank :beer great info, I spent a lot of time googling all over the internet looking for an answer.

    Russ Martin on the Yahoo/Nailheader group said he thought the sec. jets were .070, and I talked to Carmen Faso and he confirmed that, and is selling me four .070 jets to get me going. Carmen also filled me in on some of the differences between the single 4 barrel carb I'm using and the original 2x4 rear carb.

    If you've got the time, could you could you look up jet sizes for 120-256 (primary for all '65 1 and 2x4 carbs), and 120-158 (401). Also rod sizes 16-286 (front 2x4) and 16-219 (401 and rear 2x4). I've got these parts but it would be helpful to know the baseline when it comes time for tuning.

    What other Carter info do you have? Anything on venturi clusters, air valves, pump discharge squirters, and pump return springs? These are some of the items that Carmen told me may be different on the 2x4 carbs.

    Thanks again, it is much appreciated.
  4. Buford

    Buford Old guy member

    Jet sizes...120-256 is .092, 120-158 is .082. Metering rods (Carter called them step-up rods) 16-286 is .0675 X .055, 16-219 is .0685 X .063 . Pump discharge jet size is .028 for the 3645 carb and .025 for the 3921. The pump return spring has a different number for each carb, but no specs. I believe the front carb had a slightly stiffer spring as this is what closes the throttle. As for the venturis, the primaries are different and the secondaries are the same. There are 20 different part numbers for '65 AFB venturis, but no description of differences. The air valve is also a different number between the two carbs.
    I have a couple of the thick 4"-5" Carter manuals and a few smaller catalogs that have a lot of application and ID data. By the way, my '64 Buick service manual incorrectly lists the metering rods for the 3645 as 16-268. Good luck on your project! :) :) :) Frank
    P.S. Carmen is THE MAN!
  5. kustomsbykris

    kustomsbykris Member

    Im looking to try and find out what size Jets and Metering Rods went in my stock Carter AFB's ..

    3645SB....... thanks for any help you guys can give me...

  6. kustomsbykris

    kustomsbykris Member

    reason behind this is my plugs are fouling out, and the guy that rebuild my carbs noticed that the JETS and RODS were to long.. he said they were racing JETS and RODS.... thanks once again.
  7. Buford

    Buford Old guy member

    The 3645 SB has these...primary jet-.092, secondary jet-.070 with metering rods 16-286....0675 x .063. Check your first number again; it should be four numbers followed by S, SA, or SB. All AFB metering rods are the same length I believe. Frank
  8. kustomsbykris

    kustomsbykris Member

    sorry about that .. its 3578S... thanks for your help!!!!

  9. kustomsbykris

    kustomsbykris Member

    The 3578S is my primary...
  10. Buford

    Buford Old guy member

    Kris: The 3578 s is for a 1963 425 engine, and the pages for '62 and '63 are missing in my main catalog. The equivalent carb for '64 is 3665 s. Sizes are: Primary jet-.092, secondary jet-.089 and metering rod 16-167.. .0695 x .063.
    A 1963 shop manual will have these specs listed. Good luck, Frank:beers2:
  11. kustomsbykris

    kustomsbykris Member

    thank you so much for your help....

  12. kustomsbykris

    kustomsbykris Member

    I never told you what these carbs were on... I've got a 1963 Buick Riviera.. with the 425 and 2x4 had the carbs rebuilt and thats when the guy noticed the rods being longer .. thanks for all your help... I'll know who to come to next time I'm looking for an answer...


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