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Technical Carter AFB metering rod question

Discussion in 'The Hokey Ass Message Board' started by Groucho, Aug 12, 2020.

  1. Not Edelbrocks, but old school AFBs. Do you know what metering rods were in these? These are way too big, so even a decent starting point....doesn't have to be exact. I think I can figure it out, but maybe someone here's done these. I've only tuned Holleys. THX

    20200803_150147.jpg
     
    kidcampbell71 likes this.
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 49,573

    squirrel
    Member

    can't quite read the number on the carb....what is it?
     
  3. Tough getting in there now that it's back on the motor. 20200812_201615.jpg 20200812_201610.jpg
     
  4. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,389

    Johnny Gee
    Member
    from Downey, Ca

    John, is that from your newest ride?
     

  5. Yessir
     
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  6. bchctybob
    Joined: Sep 18, 2011
    Posts: 3,131

    bchctybob
    ALLIANCE MEMBER

    If you can read and post the number I’m sure Carbking can give you the original rod and jet combo. There are also websites that can get you in the ballpark but you need that number also the tag # if the tag is still on it.
    Why do you want to change it? Is it running rich? Lean? Hasn’t it been using the current setup successfully for a while?


    Sent from my iPad using The H.A.M.B. mobile app
     
    pitman likes this.
  7. Way too much typing, but i can't believe anyone drove this car with it's MANY issues. Maybe I'll type some out in the morning.
     
    bchctybob likes this.
  8. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,389

    Johnny Gee
    Member
    from Downey, Ca

    Zoomed in on the stamped number. If it's B/6804S ? (which doesn't make sense) I come up with nothing. Did find a site that had a Pontiac #'s column but the list just ended there. :mad:
     
  9. No big deal John. I wouldn't think there would be a big variation from one AFB to another, so I'm just looking for a starting point.
     
  10. View attachment 4785370
    I really HATE all this typing, but i feel like I'm being questioned and 2nd guessed here. I think some old hot rods just get displayed and not driven. This is sure one of those! Someone lowered the front to where it was bottomed out, ZERO travel. Not only rode like a rock but the tie rod was wedged against the crossmember....to the point it was in such a bind the drag link is now permanently bowed from trying to steer it. Bowed to the point the steering wheel's now off center. Solid lifters set so loose (more than DOUBLE the lash) because he said he liked the sound of solids. So loose it sounded like a jack hammer, even thru some very very thick cast aluminum valve covers. I couldn't imagine what it'd sound like thru stock tin valve covers! Not to mention some very large openings around the brake pedal and steering column it sounded like that jack hammer was in my lap! Now, the 4 speed hydro throttle pressure linkage was adjusted so far off the trans hung in 2nd gear til you let off the gas. Never upshifted. Imagine what THAT sounded like at very high RPM waiting for the fucking thing to shift with the solids set beyond double what they're supposed to be and those gaps in the floor boards letting all that NOISE in the car. It was fucking horrible. Now to the carb. The metering rods just barely fit in the jet (not correct!), allowing no fuel to the idle circuit. The idle mix screws do nothing (YES, I cleaned the emulsion tubes) and the idle speed screw is in so far that it's idling(?) off the main metering circuit instead of the idle circuit. What a mess.

    20200807_215006.jpg
     
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  11. carbking
    Joined: Dec 20, 2008
    Posts: 3,127

    carbking
    Member

    Just looking at the pictures, difficult to tell; however:

    One number might be 3361s (front carb on 409 if not a restamp, which it may be).
    Other number might be 3804s (rear carb on 409 if not a restamp, which it may be, but definitely modified). Cannot tell for sure if the castings match.

    As far as not a big variation???

    The high vacuum (cruise) step varies from 0.051 to 0.079.
    The low vacuum (power) step varies from 0.040 to 0.07325.

    As a general rule 0.001 on cruise is considered one calibration step (29 step variation).
    As a general rule 0.0015 on power is considered one calibration step (22 step variation).

    Good luck!

    Jon
     
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  12. Check post #10 and tell me what you think. I'm sure if I "start" in the middle of the numbers you provide I should be able to get pretty close from there. THX!!
     
  13. birdman1
    Joined: Dec 6, 2012
    Posts: 1,250

    birdman1
    Member

    The diameter of the hole(jet), minus the diameter of the rod. That's the size you use to start with.
     
  14. carbking
    Joined: Dec 20, 2008
    Posts: 3,127

    carbking
    Member

    With absolutely no offense meant to you:

    You mentioned the car had other issues. One issue that plagues novice Carter carburetor builders is they look at the primary bore being smaller than the secondary bore, and determine the primary jets must be smaller than the secondary jets.

    Since Carter uses metering rod technology, the primary jets on WCFB's and AFB's are almost always larger than the secondary jets. This is NOT true of the newer TQ's as they have huge secondaries.

    If I had a dollar for every WCFB and AFB that came in to my shop because it wouldn't run WITH REVERSED JETS, I could buy an island somewhere, and retire! ;)

    Might be worth-while to look at the jets, if you did not remove them, to see what the PO did with them.

    Jon.
     
    bchctybob and jimmy six like this.
  15. Did you read #10?
     
  16. carbking
    Joined: Dec 20, 2008
    Posts: 3,127

    carbking
    Member

    I did read post 10, several times, and it did not answer the question. Correct rods MIGHT just barely fit in secondary jets.

    Jon.
     
    Elcohaulic likes this.
  17. OK let's try a different angle. I get 0 response from both idle mixture screws and all the passage ways and emulsion tubes are clear. Any thoughts on that?
     
  18. Don't the metering rods go in the primary jets?
     
  19. pitman
    Joined: May 14, 2006
    Posts: 5,097

    pitman

    ^^^;)
    And too, the primaries on rear carb, often were source of mixture, actually feeding. Front carb? Looks. Rear secondaries? Vacuum called, IF needed.
    My exp. was running them on SBC's
    Your's is a larger cube GM, factory pairs, had no idle jets in fwd carb.
     
    Last edited: Aug 13, 2020
  20. What he is saying is that if someone had the secondary jets installed in place of the primary jets, the metering rods might still fit in, but not allow enough flow. At least that’s what I think he is saying .
     
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  21. bchctybob
    Joined: Sep 18, 2011
    Posts: 3,131

    bchctybob
    ALLIANCE MEMBER

    Hey Groucho, no 2nd guessing or judgement, I’m a huge fan of that car and the fact that you got it and just wanna help. We just need a little more info and current status. I can certainly understand your frustration at this point.
    I think Jon has a good point, the primary jets probably got swapped with the secondaries in a previous rebuild. That would be my first look. As for the mixture screws, once the jets and rods get back into the ballpark you may find they will start to work right too.


    Sent from my iPad using The H.A.M.B. mobile app
     
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  22. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,389

    Johnny Gee
    Member
    from Downey, Ca

    Just peaked my interest is why I looked. I also have not played with that style carb either. Any little fact I can pull in is worth something to me.
     
  23. saltflats
    Joined: Aug 14, 2007
    Posts: 10,904

    saltflats
    Member
    from Missouri

    If the idle screw is in to far you wont have any idle mixture adjustment.
    Can you read us the numbers off the carburetors?
     
    carbking likes this.
  24. I'm trying to remember where the AFBs, and AVSs for that matter, picked up their fuel for the idle circuit. I'm not sure if the primary jets and metering rods really have much if any effect on the idle mixture.

    Maybe @carbking will check in here again.
     
  25. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,389

    Johnny Gee
    Member
    from Downey, Ca

  26. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,389

    Johnny Gee
    Member
    from Downey, Ca

    Looks like your on the right track per above photo I just posted from the beginning. Rod/rods choking off idle circuit?
     
  27. pitman
    Joined: May 14, 2006
    Posts: 5,097

    pitman

    Seems I recall idle screw adj's range from 1-1/4 to 1-3/4 from (Gently) close.
    Your warranty may vary!
     
  28. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,297

    sunbeam
    Member

    I didn't think a front 409 carb had idle curcuts or choke.
     
    pitman likes this.
  29. Ok guys, I picked this up from a buddy earlier. Since the carb # not legible, how about some common jet/metering rod combos? I'm pretty sure the idle circuit gets fuel from the area between the jet orifice and higher step on the metering rods (hi vacuum). So, what is a good metering rod to jet combo? THX! 20200813_145123.jpg 20200813_151149.jpg
     
  30. saltflats
    Joined: Aug 14, 2007
    Posts: 10,904

    saltflats
    Member
    from Missouri

    Helps to know what size the carburetors are.
     
    swade41 likes this.

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