Holley issue

Discussion in 'Fuel and Air Systems' started by mopar head, Dec 2, 2018.

  1. mopar head

    mopar head Well-Known Member

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    4160 750cfm vac. sec.
    Secondary plates always wet, primary dry.
    I`m thinking this is why I get a backfire on cold starts.
    Float setting seems good.
    Anybody ever have this issue and figure it out?
    I thought it was dripping from boosters, dabbed with paper towel pieces and dry?
    Laced a strip across under both and checked after a few hours and dry...
    How/Where, else could fuel keep the secondary plates wet looking all the time?
    I cant find any sec. metering block cutaway views to help diagnose.
    Thanks
     
  2. dano

    dano Evil Handy Man FABO Gold Member

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    History of the carb? New? Rebuilt? Used and just trying it out? Etc. Have you look the linkages over to be sure they are no bent or messed up in some way. Manual or electric Choke?
     
  3. mopar head

    mopar head Well-Known Member

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    New, well only a 1000 mi. on it but has backfired on cold startup from the git.
    Electric choke, I`ll give the linkages a look see, but I never abused it.
     
  4. Treblig

    Treblig FABO Gold Member FABO Gold Member

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    Backfire could be timing....also Hollys have a habit of dumping fuel from the secondary bowls into the secondary venturies when you make a fast stop. I had to install overflow tubes on mine to keep fuel from spilling out of the vent tube on the secondaries.
     
  5. mopar head

    mopar head Well-Known Member

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    Never heard of that either. I avoid making fast stops, and the car never backfires on warm restarts. I`ll check the vent tube.
     
  6. '63GT

    '63GT Well-Known Member

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    This is fairly common to see on Vac Sec carbs. In my experience anyway....
    On a vacsec carb, the secondary's slap closed by the diaphragm spring when you close the throttle, and the fuel flow doesn't stop right away and floods the tops of the throttle blades.
    However, if you didn't get all of the way into the secondary's, you could have another problem.
    To check this:
    With the engine off, open the throttle 1/4 to 1/2 and hold it there. Now check to see if the secondary's stay closed on their own, or pull open a bit. (there's a link that forces the secondary's close at an idle)
    If not, there's a couple of things that could be the cause. 1. wrong length Sec diaphragm rod. (too short)
    2. Sec Dia spring is not returning the diaphragm to 'closed' (could also be stiff/old rubber dia)
    3. and of coarse a binding shaft. In this case, the secondary's won't open correctly either.

    My 2¢
     
  7. mopar head

    mopar head Well-Known Member

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    Could your procedure be checked cold?
    Carb was bought new, no modifying yet.
    Car can set for a week and the sec. blades look wet. ?
     
  8. '63GT

    '63GT Well-Known Member

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    Yes, it could be checked cold...
    But if its doing that over night, the float is too high. (cold back-fires is chokes system is too lean)
     
    • Agree Agree x 1
    • mopar head

      mopar head Well-Known Member

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      I`ve checked the level hot and cold, running and not, seems to me fuel would run out of level port if float was too high? It does not.
      Interesting that a cold backfire from being too lean, I`ll experiment with that.

      Thanks for the tips fellas, I`ll update with results
       
    • Treblig

      Treblig FABO Gold Member FABO Gold Member

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      Could you post some good clear close up pics of the secondaries/?? Maybe someone will see something that you're missing??
       
    • mopar head

      mopar head Well-Known Member

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      I`ll do, cause it does look like a hole in the center of large hole venturi`s looks to have a tapered sleeve that maybe missing a cap? maybe not.
       
      Last edited: Dec 2, 2018
    • mopar head

      mopar head Well-Known Member

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      Don`t know if this is helpful. IMG_20181202_201429.jpg
      Wondering the purpose of the center boss with hole is for between the boosters?

      IMG_20181202_201418.jpg
       
    • Treblig

      Treblig FABO Gold Member FABO Gold Member

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      On my Holley that hole is where the center squirter is located:

      DSC07926.JPG DSC07927.JPG

      If it's missing the center squirter fuel will pour out into the secondaries without any metering.
       
    • mopar head

      mopar head Well-Known Member

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      Does your`s have a secondary accelerator pump?
      Mine does`nt
       
    • Treblig

      Treblig FABO Gold Member FABO Gold Member

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      Mine only has the front pump...no rear pump. Going to bed so I'll have to continue this tomorrow. treblig
       
    • dano

      dano Evil Handy Man FABO Gold Member

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      Looking on Holley's site, none of the pictures of a vacuum secondary 750 have a center squirter. They look like Mopar Head's carb.

      Are you running a pressure regulator? I had an issue with a Demon carb over fueling at idle and it turned out the Holley mechanical pump I had put out way to much pressure and was over running the needle and seat. Stock pump fixed the issue.
       
    • mopar head

      mopar head Well-Known Member

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      No regulator, bought new replacement pump, but it had a down pointing outlet compared to the original? pump. Dont know if their were different pressure applications for different 440s, I would think not. Motor was a non HP 72 car engine. I have a port for a gauge in the inlet manifold, probably should buy one and verify.
      I`ve run the car many times, pull in shop, and check for dripping and never see anything.
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      If the pump has a spring that creates too much pressure, you'ld see it as overfilling bowls. That as you know would in turn result in in high level when you opened the sight plug and dripping from the boosters (or worse).

      The throttles are below the seam with the main body. Off the top of my head I can't think of any passage on the secondary side that would let fuel come through there even with a bad or incorrect gasket. If I think of one I'll post. Its possible there's casting porosity.

      The most likely explanation I can think of right now is fuel condensation. If you don't see it while running, but only when shutting down, give that some thought. The plate is cool, air is no longer flowing. Vapors condense out onto the surface.
      Some posts about that at RFS. Here's one.
      Capillary Action?

      Here's another, in this case when engines are running.
      Wet Palm
       
      Last edited: Dec 2, 2018
    • mopar head

      mopar head Well-Known Member

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      Agree on the passages Mattax, I remember one time after bringing home after shutdown, I noticed quite a bit of vapor/smoke? wafering out of the left tailpipe, same pipe that seems only to get the cold start backfire. Something to ponder...
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Deleted as it was refering to backfire into the intake.
      OK. Need to think about it different since its backfire in the exhaust.
      Too rich and possibly combined with late timing.
       
    • mopar head

      mopar head Well-Known Member

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      No movement of secondaries
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      That is simply the boss for secondary squirters. Not used on any vacuum secondaries I've seen except the one posted by Treblig.

      Worst case, if its really leaking (should see that by fuel level dropping when the engine is shut off) might have to take it apart and look.
      Sometimes even simple things like this can be hard to figure out. See last post, where he figured out where the leak was coming from.
      4412 has me stumped
       
    • mopar head

      mopar head Well-Known Member

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      On holley`s blown view file they show a little cap/plug? listed #129 as secondary bowl vent valve, but hard to discern where it goes?
      I`ve had this carb apart, just primary float bowl and put back to stock, messing with jets.
      I`ve had it upside down draining gas out etc.
      Later I found a small chrome?/shiny ball, little larger than a bb, under the car, and I could`nt figure where the heck it came from. I was wondering check ball? but holley tech says no way a check ball can fall out of this model carb... ?
      https://documents.holley.com/techlibrary_4150_4160_exploded_view.pdf
       
    • '63GT

      '63GT Well-Known Member

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      There's a check ball, or needle under the shooter, and there's a check ball under the Vacuum Diaphragm cover and also in the bowl for the shooter diaphragm, but it is retained by a small flat wire (some use a red silicone rubber valve in place of it).
      If you've had any of those apart, that's it.
       
    • mopar head

      mopar head Well-Known Member

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      I`ve had the acc. pump off to replace a leaking gasket with the blue upgrade gasket. Pretty sure the pump ball is crimped in and can`t fall out. Never messed with the vac. cover. Holley tech. says these are the only 2 check balls in the system. Parts list only state only 2 that I see. They note 70 and earlier used a ball under the nozzle.

      That ball on the floor has been bugging me since.
      Sure would be nice if someone has a modern 6140 and look if it looks the same as mine.