Problem with Holley 4 bbl

Small Block Mopar Engine

  1. dart_68

    dart_68 Well-Known Member

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    Got a problem with my 750CFM VS on my 360.

    It doesn't respond at all to idle mixture adjustments. The usually means that excess gas is entering the system. So I went through the usual suspects -

    1) Float level too high - checked and was correct just barely trickling out of the hole.
    2) Primary throttle blades opened too far - pulled the carb to check and was correct (transfer slot looked like a square).
    3) Blown power valve - checked with tester and was not blown.
    4) Fuel pressure too high - gauge shows 5.5 lbs pressure.

    What have I overlooked?

    It's frustrating and can't seem to find the problem other than something wrong with the carb that is leaking gas into the manifold. Plugs are gas fouled and I've went through 2 sets of new plugs and don't want to buy a 3rd until I find the problem. Gaskets seem perfect.

    Thanks.
     
  2. 448Scamp

    448Scamp Running Free

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    Close the throttle blades. If you can’t close them and maintain the correct idle rpm you need to recurve the distributor or drill some small holes in the throttle blades or both.
     
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    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      Has it ever run right? Does the engine die when you seat the idle mixture screws? The power valve could be OUT and it would not affect idle since no signal is at the boosters to pull fuel in. So you can rule the PV out even if it's buster all to hell. If it doesn't die with the air screws seated, it's definitely too rich. Probably needs leaning out on the idle circuit. Does it have adjustable air bleeds and fuel restrictors?
       
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      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        How does anything continue to idle with the throttle blades completely closed? You're losing me somehow. Where will it get air from?
         
      • 448Scamp

        448Scamp Running Free

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        I didn’t mean to close the throttle blades all the way. He is idling on the transfer slots so he needs to do what it takes to close the throttle and get it back on the curb idle discharge ports.
         
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        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Well you did say "close the throttle blades" lol.
           
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          • 413

            413 Well-Known Member

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            How much idle vacuum does it have? What power valve does it have? Is it the correct valve? Rebuild the carb.
             
          • Gator

            Gator Mopar or No Car

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            Tear down the carb and clean it completely. You prolly have some hidden dirt particles in your bowl or perhaps a partially plugged jet. I experienced pretty much the same thing that you have described with my 750 eddy and that is what I did. Carb functions well now and car runs great... Good Luck to you.
             
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            • jazak5

              jazak5 Well-Known Member

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              ditch the holley and go avs 2
               
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              • dart_68

                dart_68 Well-Known Member

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                The primary throttle blades are closed up so as to only show a very small portion of the transfer slot. As per previous tuning threads what you see is that the transfer slot looks like a square when viewed from below.
                 
              • dart_68

                dart_68 Well-Known Member

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                Nope, stays running. No reaction at all to mixture screw changes.
                No adjustable air bleeds. Just a stock Holley 3310.
                My understanding of the Holley PV is that at idle the PV has no affect on enrichment since it only adds fuel via the boosters. However, a blown PV can leak fuel past the diaphragm though the vacuum port and into the manifold.

                The wrong PV can cause problems when transitioning from idle to the mains. At least that's what I've been told.
                 
              • dart_68

                dart_68 Well-Known Member

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                I'm going to pull the carb again and go through it, each passage, etc. to make sure everything is as it should be. I have 15* initial advance (not a stock cam) and it seems to like that. I've been adjusting the idle speed via the secondary set screw instead of the primary as I've read on this forum. I did make a change to open them up a bit and I wonder if I went too far. It currently idles at 1000 and would like to get it down to 700-800. I don't know if that much opening would be too much or would have any affect on the primary idle metering circuit. I guess it could the same way it could if the primaries were open too far...pull fuel from the boosters.
                 
              • 413

                413 Well-Known Member

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                Do you have an idle circuit on the secondaries? 4 mixtures screws? If not then that’s a bad sign, no wonder the mixture screws do nothing, and it’s rich. You just identified a BIG problem. Yes in your first post you tell us “excess gas is entering the system” You just nailed it. At idle the fuel needs to go through the idle circuit for the mixture screws to do anything. You are bypassing the idle circuit.

                If your plugs are fouled again you will need new ones again.

                What is you idle vacuum and what power valve? It will add fuel all the time if it’s the wrong one.

                There are many unanswered questions here.
                 
                Last edited: Aug 3, 2021
              • brian6pac

                brian6pac Well-Known Member

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                Close the primary throttle blades some till you get the idle down to 600 or 700 rpm and see if the mixture screws start working. Squaring the transfer slot is a good starting point but not the spot were it has to be.
                 
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                • Cuda416

                  Cuda416 Well-Known Member

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                  I had a similar problem with an 1850. Someone before me did a crap job "rebuilding" it and lots of stuff was clogged up. Once I cleaned and rebuilt it properly it worked great (until a vacuum leak developed) under the manifold.

                  You might have a bad float needle/seat, or something interfering with it's operation.
                   
                • Cuda416

                  Cuda416 Well-Known Member

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                  I didn't see where anyone asked where the gas is leaking from. Can you see the source? I think it might be possible to cause a problem like this is the throttle plate gasket is 90 deg out. Someone can correct me if I'm wrong.
                   
                • dusted

                  dusted FABO Gold Member FABO Gold Member

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                  If the power valve is blown it will idle with the mixture screws all the way in.
                   
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                  • Daves69

                    Daves69 Well-Known Member

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                    The plot thickens.............
                    I was going to ask if the carb had been rebuilt and if the secondaries are possibly hanging up on ya'.
                     
                  • Cuda416

                    Cuda416 Well-Known Member

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                    Yup, missed that. Close them back up and get it running "normally" first.
                     
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                    • beanhead

                      beanhead Well-Known Member

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                      You verified the T-slots aren't overexposed and the PV tested out okay, that's good. Make double sure the PV is clearing everywhere and it's gasket/gaskets are sealing well. Check for throttle binding. There's only so many places fuel can sneak into the intake so check or replace all your gaskets too.
                       
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                      • 448Scamp

                        448Scamp Running Free

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                        Yeah, I was clear as mud on that one!
                         
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                        • 448Scamp

                          448Scamp Running Free

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                          Then you could have some other issues. One I found a lot on older Holley stuff was the power valve will hit the boss in the main body. This holds the metering block off the main body and you get a leak, and the PV gets blamed. The same type of issue can happen if the main body or the metering block aren’t flat. I’ve seen both be pretty warped. If you can close the throttle blades all the way and the engine keeps running you are getting air somewhere. Also, have you verified where the secondary throttle blades are and how much they are open?
                           
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                          • DJC

                            DJC Well-Known Member

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                            If it's leaking alot of gas down the intake, check the gasket between the metering block and the body. IF you put the wrong one in, there's passage above the power valve that isn't sealed properly. Images below

                            This is the right type with the small hole isolated right.jpg

                            And this one is the type that can cause the leak wrong.jpg
                             
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                            • dart_68

                              dart_68 Well-Known Member

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                              It has the upper gasket. I think the lower one is used on some Holleys that have a tube for the accelerator pump circuit.

                              An update...after I took the carb apart and blew out all the passages, rechecked the PV, and put it back on, I fired it up and after it warmed up I turned in both idle mixture screws all the way in. Not only did it not die but actually sped up. So, it did respond to mixture screw changes but only when I leaned it out as far as I could. It has a 65 PV but only pulls 5" vacuum at idle. That should mean the PV is open at idle but it shouldn't (key word) be pulling fuel from the boosters with the primaries almost completely closed (just a "square" of the transfer slot showing).
                               
                            • RustyRatRod

                              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                              What about the secondaries?
                               
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