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Technical Carter AFB metering rod question

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

  1. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    I run 60/72 rods 109 primary jet 95 secondary jet in two 625 F/M Carters on top a 460 inch 409 with a Mquillen Intake. Not sure that's much help.
     
    Groucho likes this.
  2. Yes, I got that too after I thought about it for a moment. After all the information last night I had to take a step back and re read some of it. Im more inclined now to believe someone swapped the jets, making it very hard to get the metering rods in because now that I got the strip kit from my buddy my rods aren't much bigger if at all than the rods in that strip kit. Thanks again everyone. More tomorrow.
     
    bchctybob likes this.
  3. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

  4. OK the big jets are upfront and are right around .l00. The rods are close to .062 and .068 which all seems close to normal according to the chart above. All orifices and emulsion tubes clear. Why does it seem like no fuel is getting to the idle circuit? And here's how far the speed screw is in. Stumped! Thank you. 15974417772595086580509501720790.jpg
     
  5. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    Flip it over and see what the throttle blades looks like, are they passed the transfer slot?
     
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  6. 20200814_150945.jpg 20200814_150938.jpg
     
  7. They are open pretty far, which is what I expected because I believe it's idling on the main metering circuit because no fuel is getting to the idle circuit in my opinion.
     
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  8. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    Looks like its passed the slot
     
    bchctybob, 427 sleeper and Groucho like this.
  9. I'm convinced no fuel is getting to the idle circuit but I can't figure out why. I removed the venturi clusters and sprayed Gumout with that little tube in all the little orifices and everything is flowing as I believe it should.
     
  10. Wrong venturi to main body gasket?
     
  11. There's really not much to it. I was wondering if it had the wrong venturi clusters. Since the front carb (dual quads) has no idle circuit, are the venturi clusters different and are they interchangeable. These don't seem to be for no idle circuit but who knows? 20200814_161634.jpg 20200814_161644.jpg 20200814_161705.jpg
     
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  12. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    Don't think it will get much idle mixture with the throttle blades open that far.
    I,m not sure what you are working on. If you are running two 4s and both have idle circuits it is going to be a balance between the two.
     
    swade41 likes this.
  13. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    Did you post pictures of both carburetors, I thought I seen two different # carburetors and both had idle mixture screws.
     
  14. It's got 2 fours, with no idle circuit on the front carb, that and it's blocked off so I don't get any problems from it while trying to tune the rear carb.
     
  15. I know you know how to map out circuits. Your most likely right that the cluster is the issue. Try putting a wire into flat air bleed (no tube one) as a restricter to see if it helps pull fuel up center tube.
     
    ClayMart likes this.
  16. When may have been typing at the same time so check out my post above.
     
  17. saltflats
    Joined: Aug 14, 2007
    Posts: 10,843

    saltflats
    Member
    from Missouri

    Okay, I went back and looked a the pictures and see it is a blurry shot of the same one.
    Can you give it more timing to get it to idle up and back off the idle screw and turn the mixture to say around 1 and 1 half turns out from light seat.
     
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  18. I'll try that in the morning, thanks. All other ideas are welcome.
     
  19. ^THIS^ ;)

    Or just block the idle air bleeds temporarily with a piece of tape or your finger. Easy, free and no irreversible modifications made to the carb. And it won't hurt to try getting the throttle blades closed a little further.
     
  20. Failed to read photo's. I thought you were holding throttle plates open for a visual. Instead they've been open my bad.
     
    Last edited: Aug 15, 2020
  21. I'm not familiar with the air bleeds on a Carter as I am on a Holly.
     
  22. Actually transfer slots are feed via the idle circuit. So there is fuel in the circuit but it's uncontrollable because throttle plates are open so far. Basically it's hemorrhaging fuel.
    [​IMG]
    Does the engine have a cam with lot's of duration and want's more air than carb/carbs can give it at idle?
     
    Last edited: Aug 15, 2020
  23. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,208

    Elcohaulic
    Member

    Once you get the hang of the Carter AFB you will come to love it.. It was so simply engineered and they run real good.. They are so easy to troubleshoot and rebuild..
    I always wanted to make a dual feed air horn for one...
     
  24. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,208

    Elcohaulic
    Member

    I had one car that the owner could not get running right. Here the Carter never put the spring in the passenger side power piston..
     
  25. carbking
    Joined: Dec 20, 2008
    Posts: 3,091

    carbking
    Member

    One more time:

    Since the carbs are obviously off (to picture the underside); how about either posting clear pictures of the part numbers or reading the numbers and posting the numbers? I guessed, based on being able to read a couple of numbers, and looking at pictures of the castings, but not positive I guessed correctly.

    Would be nice to know the application????? If I guessed right, then 409 Chevy dual four. What kind of modifications have been made to the engine?

    Would also be nice to know the numbers on the primary venturii clusters. IF these are 3361 and 3804 carbs, the primary venturii look very similar for the 2 carbs, and will physically interchange, but will not functionally interchange (idle issues).

    Would be nice to know the numbers stamped on the metering rods??? The sizes are important, but so are the profiles. Rods of the exact same diameters, but different profiles are physically interchangeable, but not functionally interchangeable. Knowing the rod numbers would allow us to know if these rods will work in the carbs (if we knew the carb numbers). I am aware of 19 different rod profiles, and there may be more.

    Pictures of the carb flange mounting gasket(s) would also be useful. MANY of the FLAPS rebuilding kits supply an incorrect mounting gasket, causing a vacuum leak, and a very lean idle. Have you checked these gaskets against both the intake, and the carburetor bottoms to assure there is no leak?

    And as others have mentioned, having the throttle positioner screw adjusted as pictured, with the plates open so wide, functionally removes the idle circuit from the carburetor. The air velocity past the idle ports is insufficient to create the appropriate negative pressure in the idle circuit because of the plate opening.

    These carbs are some of the better 4-barrels ever built, but Carter built 505 different versions. In 60 years of working on these, the most serious problems I have seen (other than burn out on some that required the stainless plate) is parts being interchanged that should NOT have been interchanged.

    Jon.
     
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  26. carbking
    Joined: Dec 20, 2008
    Posts: 3,091

    carbking
    Member

    Some of the air horns would be fairly easy to modify, however not sure why it would be necessary. Standard fuel orifice was 0.099 inch on street performance models. Valves with orifices up to 0.120 (25-1067U) were/are available. This gives an increased fuel flow of 46 percent.

    Jon.
     
  27. I changed the base gaskets from the wrong ones that looked like they were working fine to correct ones and no changes. This I expected. 20200815_064219.jpg 20200815_064117.jpg 20200815_064038.jpg
     
  28. I have to admit, this last time I really was hoping that the primary and secondary jets were switched as suggested.
     
  29. As far as what's in the motor, I have no idea since it was built near 60 years ago. It does idle like the cam is mild.
     
  30. carbking
    Joined: Dec 20, 2008
    Posts: 3,091

    carbking
    Member

    If the venturii clusters pictured are in the 3804s, they are incorrect.

    The correct ones should be stamped 799 and 800.

    637 and 638 were used on the 3362s.

    A bit of history: the original dual quads on the 409 had 3361s (front), and 3362s (rear). The 3362s was superseded by 3804s because of idle issues. A few other calibration tweaks were done at the same time. The primary venturii clusters contain much of the idle circuit (idle jet, idle air-bleed, idle restrictor, and idle bypass).

    Guessing again, that this carburetor was at one time "rebuilt" by one of the commercial carburetor "rebuilders" that interchanged some parts they should not have interchanged.

    However, the engine should still idle, albeit not perfectly, on the idle circuit. I don't think the incorrect primary venturii are all of your issues; but with these being incorrect, the entire carburetor is suspect.

    Sorry to be the bearer of bad tidings.

    If you put it back together, and try it (assuming you have a relative stock cam in a relatively stock 409):

    Try:

    (1) block-off plate on the front (leave the front carb on the bench)!
    (2) back out the throttle positioner screw until the plates close, now turn it in to crack the primary throttles open.
    (3) Turn the idle mixture screws in until they are thumb tight, and then back them out 1 1/4 turns.
    (4) Start the engine, and PHYSICALLY run the engine at a high idle until normal operating temperature.
    (5) See if the engine will idle.

    EDIT: before re-installing the carbs, check the lower idle ports on the 3804s to see if some heavy-handed "mechanic" has overtightened the screws, and cracked the lower idle port discharge area (inside the throttle bore). This area seems to be quite thin on Chevrolet AFB's (or there are more heavy-handed Chevy mechanics ;) ). I have seen many of these where the discharge area was cracked. If so, it must be welded and re-machined.

    They do look OK in the picture, but picture might not show a crack.

    Jon.
     

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