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Technical Carter AFB metering rod question

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

  1. The front carb has been blocked off throughout all this. Lower idle ports appear to be fine. Is it worth looking into the other carb to see if it has the right venturi clusters? From what you're saying, although mine are wrong it should still idle on the idle circuit(?) Thanks for all your time on this. I'll go out there in a couple hours and resume work
     
  2. carbking
    Joined: Dec 20, 2008
    Posts: 3,091

    carbking
    Member

    The venturii clusters in the front carb are different from either of the rear carbs.

    Jon.
     
  3. If I put it all back together and I still cannot get it to idle on the idle circuit what would you suggest I try next? Thank you
     
  4. Are the metering rods and jets I mentioned earlier close enough to being compatible for now?
     
  5. carbking
    Joined: Dec 20, 2008
    Posts: 3,091

    carbking
    Member

    Don't know, need the numbers on the rods.

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

    carbking
    Member

    If it won't idle at all on the idle circuit, then more testing is in order. You have assumed the carburetor is the issue, it may be something else.

    (1) Compression test
    (2) Poor idle is a classic example of a electronic whizbang in the distributor, and less than desirable primary voltage. Once the RPM is sufficient for the voltage to pickup, issues go away.
    (3) Vacuum at idle (the first aftermarket timing set I personally installed had 3 marks on the gear), put the engine together, and had poor idle, but lousy vacuum. Took it back apart, and found a 4th mark. Used that mark, and ran perfectly. Graduate of the School of Hard Knocks!

    If all of the above are good, then a different rear carb (and before you ask, I am sold out).

    Jon.
     
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  7. Interesting you say this. It has a magneto in it that I am getting rid of and replacing with stock points distributor soon. Maybe now sooner than later. Thanks again
     
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  8. These rods are pretty fat looking (.062 .068) and I'm kind of reluctant to put them back in 20200815_095027.jpg
     
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  9. I've never seen rods as stubby as the ones pictured above, so I'm going to guess at 1 of these more typical profiles to put back in instead. 20200815_095940.jpg
     
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  10. 6sally6
    Joined: Feb 16, 2014
    Posts: 1,586

    6sally6
    Member

    Yeah.......I would swap those metering rods out for a set of your other ones. I agree.......(I'm no guru fer sure but) those look like someone ground the ends off flat!
    Try different springs(prolly lighter ones) especially if it has a fairly snotty cam.
    Twist in a bunch of initial timing too....just to get it to idle higher, and try tuning from there.
    Let us know what happens.....
    6sally6
     
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  11. Do you think the tip of that metering rod is broke off inside there ?
    Did you ever close the throttle blade gap to get it back into the idle circuit ?
    If you go on Edelbrock's website they have a tuning section, you can print out the tuning manual, figure out what size your carbs are and cross reference it to the Edelbrock to get a base jet, metering rod and spring.
    Always pull the metering rods before taking the top of the carb off and always put them in last, leaving them in while you take the top on and off will bend the rods and also break the tips off like those ones you show.
     
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  12. If tips broke the pieces are long gone. I changed them to some that should be close. I did not close the throttle blades yet. I've got a good idea where to start (jets/rods) thanks to those posting here. And yes, rods 1st out an last in! I got word yesterday there were F-18s at a near by airport, so I dropped what i was doing and went to check it out.
    117950760_10217892345042216_4605324440226034103_o.jpg
     
  13. lippy
    Joined: Sep 27, 2006
    Posts: 5,563

    lippy
    Member
    from Ks

    Never seen metering rods that were pointy on the ends. I mean on the very ends. From what I remember the tapered part of the rod is what controls the flow. Right? Lippy
     
  14. lippy
    Joined: Sep 27, 2006
    Posts: 5,563

    lippy
    Member
    from Ks

    Did I see carb adapters?
     
  15. The 1st and smaller step is part responsible for controlling flow on the main metering circuit, and the 2nd slightly thicker step controls fuel on the idle circuit when high vacuum pulls that needle deeper into the jet.
     
  16. Fordors
    Joined: Sep 22, 2016
    Posts: 3,718

    Fordors
    Member

    3500B11E-926F-4FE9-B71A-39E1BC0FA5DD.jpeg The photo you posted shows a rod numbered as 16-124 (shown as correct for the 3804S and 3361S) and those have a step of .069 to .0635 and your measurements are very close to those numbers. I see two steps on the rod where I indicated on the photo. Nothing is broken or modified on those rods.
    In reading the thread it sounds like your jets are correct for the primary and secondary sides and your metering rods are the right number so the only other problem area would be the venturi clusters and @ carbking has addressed that. He gave the part numbers and it looks as though yours have inadvertently been switched between the carbs.
    Put the clusters where they belong, back off on the curb idle screw, and get the idle mixture screws set to a preliminary setting, I bet you will be able to get that thing to idle.
    Tighten up the valve lash too, that’s hard on the valve train.
     
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  17. Nobody has mentioned an O2 sensor to help out on this problem. Yes it's a lot of trouble to weld in a bung and they're not very cheap. But if you really want to get your carbs right on target from Idol to moderate acceleration to cruising to wide open throttle there's no substitute.
     
  18. Who needs an O2 sensor when your ass and spark plugs tell you the same thing.
     
  19. EXACTLY! After working on thousands of cars, why would I need one now?
     
    427 sleeper likes this.
  20. Looks like we have some sort of Nazi on here that deleted my last post on this subject... isn't that nice...
     
  21. ok, so here it is again, slightly edited... it's 100% simply a factual analysis without anything snotty.... soooo... is somebody going to delete it again???
    ---------------------------------------------------------------------------------------------------------------------
    Hey, Johnny and Groucho...

    Do you own a hand held volt meter? Do you own a hand held Ammeter? Does your car have a speedometer? Does your car have a fuel gauge? Does your car have a volt meter or ammeter? Does your car have a temperature gauge? Have you ever used a set of A/C refrigerant gauges? Have you ever used a compression gauge? Have you ever used a leak down tester? Have you ever used a micrometer? Have you ever used plastigage? Have you ever used a tape measure? Have you ever used a vacuum gauge? Do you think a fuel injection system is completely inoperable without an O2 sensor?

    I suspect your honest response is YES to all the questions above. Guess what.. they ALL tell you "what's going on". Same for an O2 sensor/gauge. It tells you exactly "what's going on" as you drive down the road, under all load conditions. Reading plugs was about the only thing we could do back in the 60's. Does reading the plugs tell you if you are rich or lean at idle? Does it tell you that you are rich or lean under moderate acceleration? Does it tell you if you are rich or lean at cruising speed? Does it tell you if you are rich or lean at WOT? Does it tell you whether you are running 12/1 or 15/1 in ALL or ANY of those modes as speed/loads change while going through those modes of operation? The answer, if you haven't figured it out yet, is absolutely NOT.
     
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  22. Any diagnostic tool get's you into the ball park area of where the issue is. It can not tell you exactly what part/ parts will be needed.
     
    427 sleeper likes this.
  23. Who said anything about parts? If your speedometer is sitting at 0 while you're driving down the highway you're supposed to figure out yourself what Parts you need. Holy cow.
     
  24. Oops I just thought of something. Maybe you're talking about this carburetor issue. That's when you turn to the manufacturers charts of combinations ...of rods and jets..
    .something like this. Scroll down to starting at page 10 and check out the calibration charts. I realize this is pretty difficult for some people but for most folks it's pretty straightforward...

    Google the following search.."edelbrock carburetor 1405 manual"
    Scroll to the second hit, brochure #0033, scroll again to page 10... that Page and the next few pages will tell you what parts you need if that's what you were getting at. I realize this is pretty dadgum complicated.
     
    Last edited: Aug 17, 2020
  25. And no it doesn't get you in the ballpark it tells you exactly what you need to make it right
     
  26. Not necessarily since all vehicles weigh different, have different engines, transmissions, rear end gears, different elevations where the cars are driven.
    Those charts will get you in the ball park but are not set in stone and should be interpreted as such.
     
  27. I understand, but understand this.....I've never needed or wanted an O2 senser. But I have wanted or needed pretty much everything else on your list. And I would not have deleted your post, even if I had that capability, which I think I don't.
     
  28. To Swade......WRONG... ask yourself this. Why are there dozens and dozens of combinations of rods and jets to achieve Optimum performance? ....ideal fuel/air ratio is a constant, regardless of engine, weight, etc
    Correct selection of rods/jets is what gets those variables narrowed down to the correct combustion efficiency. You are looking at this upside down. That's the whole point of correct rod and jet selection.

    Variations in the carburetor castings, fuel pressure, atmospheric pressure, engine vacuum, cam selection, throttle position, RPM, intake manifold configuration....all make it impossible for a carburetor manufacturer to give you the best performance right out of the box. Why in the world would they publish and furnish dozens and dozens of selections for the user to adjust fuel delivery as it should be?

    As a "side fact", most out of the box carbs will run rich. Do you know why?

    By the way I guess you could call this antidotal, but my 383 stroker ran pretty dang good, but after installing my O2 sensor I found that my ratios were all over the map anywhere from 10 to 20 depending on throttle position acceleration steady speed at various RPM Etc. After reading the charts as posted previously I ended up changing both sets of rods and jets and now it never gets outside of 12 to 15 no matter what I do with the gas pedal. That's a fact.
     
  29. BadgeZ28
    Joined: Oct 28, 2009
    Posts: 1,109

    BadgeZ28
    Member
    from Oregon

    I had a old model 9625 650 cfm Carter. Metering rods were 16-7347 (.0745-.047). Primary jets were 120-398 ( .098) Springs were 5 vac (Orange). Secondary Jet 120-386 (.086).
     

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