Holley stumble trouble

Fuel and Air Systems

  1. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    The old Holleys calibrations are usually close - just need a little tweaking.
    The new stuff often has newer, but not neccessarily better ideas baked in from the start. So its a pick your poison situation. For someone who knows they will be adjusting restrictions and bleeds, that's tips the scale toward the new shiny. In terms of cost, an old Holley you already own is hard to beat when compared to the priceds of new carbs these days.

    There is another option on the MAB and IAB restrictors. Press in new ones. BLP had the blanks - hopefully they still do.
    Years ago I paid one of the guys turn a couple in the machine shop. (Like many shops in a larger setting, the machinists could do their own small side jobs on their own time.) Should have had him make more - like a dozen!

    Obviously this isn't an easy change option, but if your close and drilling up, then need to close down, its a nice solution instead of having wires permanently in there.
    On a carb with choke tower, tapping and using a set screws is a PIA. So this is the situation where IMO its worth considering the press-in option.

    my ,02
     
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    • mderoy340

      mderoy340 Well-Known Member

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      Before you pull the carb off hookup a tach and slowly bring the rpm up to see what rpm the primary boosters start to flow. Don't be surprised if one side starts flowing sooner than the other if you are using a dual plane intake. Also bring the rpm to 2k and see if the motor runs cleanly, this would be the upper side of the idle transition circuit, you are looking for a lean misfire. All this is done in nuetral. When you check the emulsion well holes in the metering block you may find one or more plugged with crap.
       
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      • yellow rose

        yellow rose Master Of Insanity

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        This is a great idea. One thing I learned is the boosters come on differently with load verse no load. It’s hard to load a clutch engine to see the boosters come on.

        The stick guys I know either mount a camera and drive the car and watch, or they verify what’s happening on the dyno.

        The converter guys can just bring the engine up and watch. You just have to be careful and not kill the converter.
         
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        • SSG_Karg

          SSG_Karg Heeeeeres Johnny!

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          The driver side booster comes on at 2050 rpm and the passenger side doesn’t come on until 2250. Runs smooth as a sewing machine though. Gonna let it cool down and pull it apart.
           
        • SSG_Karg

          SSG_Karg Heeeeeres Johnny!

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          • Hysteric

            Hysteric Well-Known Member

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            Now disconnect the shooters and block the primary boosters and drive it on the transfer slot to see where that ends. From memory you can use some plasticine or paper to do it. If the transfer slot runs out sooner you can raise the float level to get the primary's to come in sooner.
             
          • SSG_Karg

            SSG_Karg Heeeeeres Johnny!

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            How do I block off the boosters?
             
          • Hysteric

            Hysteric Well-Known Member

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            You need to pull the metering blocks to do it.

            Its a lot easier with an AFB carb where the boosters just unscrew. I actually just jb welded an old booster from another carb so i can just swap them in when i need to.

            You just need to do it once then remove it.
             
            Last edited: Jul 25, 2020
          • SSG_Karg

            SSG_Karg Heeeeeres Johnny!

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            Primary metering block. Anything look wonky?

            C1836160-E794-4B13-BACF-CD0623021B99.jpeg

            5A67AD31-1141-4FE4-9D53-6ED4F6BF79DB.jpeg
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Maybe.
            See the holes in the upper doglegs?

            Originally those were for the "emulsion tubes". If the e-holes in the channel are bored through, then odds are there is no emulsion tube.
            Another check for the tube is to look at the top of the meter block. My understand is the tubes have top that flush because its a solid brass piece.
            Otherwise the wells are sealed with a cap.

            I htink I posted a link to photos earlier in the thread. if not I'll find it.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            OK. I mentioned it but didn't link anything because I was trying to keep focused on normal, basic stuff.

            I'm borrowing this photo "Tuner" posted here on RFS.
            It shows the emulsion tube removed.
            106_434eeb186c86f9dc01c34448312395da.jpg

            Unfortunately, some blocks were made with the hole for the emulsion tube even though they didn't have.
            Air can be introduced into the main well either through a tube, or through drillings in the casting. but not both!

            When the connecting hole for the tube is in the dogleg but there is not tube, sometimes weird delays occur.
            After Mike and Tuner discussed this problem, I went back and fixed my 650 VS.
            So here's another thread on it, along with my attempt to explain the issue.
            Another dogleg kill bleed carb - list 80783, 650 VS

            However before jumping ahead, lets make sure there is no tube. If tops of the wells are plugged with caps, theat will be another clue there is not tube.
            Sometimes the bottom of a tube is visible when the jets are removed.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            White arrows show the air getting into the main well from drillings in the channel (air well).
            upload_2020-7-27_23-4-36.png
            photo of cutaway is Yellow Rose's work.

            With a tube, air goes between the two seals, into the hole, and comes out through the small holes on the side of the tube.
            Apparently that allowed for some more specific calibrations on factory carbs.
            upload_2020-7-27_23-12-51.png
             
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            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              I don't know if this helps but here was an attempt to illustrate the fuel and air flows at mid to high rpm, full throttle.
              upload_2020-7-27_23-15-22.png
               
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              • 512Stroker

                512Stroker We are all here because we are not all there.

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                It's complex to say the least
                 
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                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  Found the version showing the begining of main system flow. (Idle/transfer not shown).

                  Blue represents fuel. White arrows represent air flow from main air bleed.
                  It shows how the fuel from the bowl, and how air injected in the correct location can help move the fuel out of the well toward the booster.
                  upload_2019-9-13_11-16-17-png.png
                   
                  Last edited: Jul 27, 2020
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  I think looking at the cutaway is more difficult than the line drawings, but regardless, yea.
                  This might have been one of those times the explanation might be a big distraction.

                  Bottom line is that if there is no tube, then the dogleg holes should be plugged.
                   
                • yellow rose

                  yellow rose Master Of Insanity

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                  Ok, those holes up high like that are for emulsion tubes and not the drilled emulsion channels. That means the OP has emulsion tubes OR the block was drilled like it was getting tubes and didn’t get them and it was sent out like that.

                  Did I get that right?
                   
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                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    Yes! :)
                     
                  • SSG_Karg

                    SSG_Karg Heeeeeres Johnny!

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                    So how can I tell if there’s tubes in it?
                     
                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    Lemme rrewrite this, hopefully more clearly.

                    1. There are two large starter holes in each airwell. That's the channel with the dogleg. With a good light, and preferably with the drills or pin gages, check if there are holes drilled in the bottom of each one. They should be around .026 to .027" diameter. If the e-holes in the channel are bored through, then odds are there is no emulsion tube.
                    2. Look at the top of the meter block. See if there are cups or flat caps sealing the drilled wells. The inner pair are the main wells.
                    3. Remove the main jets and peek into the main well. Sometimes the bottom of the tubes are visible.
                     
                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    Another shot at trying to explain the issue...

                    If the top of the main well is sealed, no kill bleed, no hole at in dogleg;
                    Then the first place air bleeds through into the main well is the upper e-hole.
                    This air helps lift some fuel into the angle channel leading to the booster.
                    upload_2020-7-28_10-17-4.png



                    Our theory is a hole in the dogleg creates an easier path for the air to flow. So instead of the booster pulling on fuel, it pulls on air.

                    upload_2020-7-28_10-21-17.png

                    To be complete here, when a siphon break (aka kill bleed) is drilled into the angle passage, it sometimes actually helps start the booster flow. That's because its blowing in the correct direction. So it may cause a little delay, but then makes for a more consistant initiation. Size also matters.
                    upload_2020-7-28_10-34-3.png
                     
                    Last edited: Jul 28, 2020
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                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      Seeing this I'd assume no tube.
                      upload_2020-7-28_10-46-13.png

                      But looking at the blocks on this carb, I'd expect the primary to have e-tubes.
                      upload_2020-7-28_10-48-14.png
                       
                    • mderoy340

                      mderoy340 Well-Known Member

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                      What is the part number stamped on the metering block you have? Have you checked the size of the holes yet?
                       
                    • SSG_Karg

                      SSG_Karg Heeeeeres Johnny!

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                      I’ll post more pics of the metering block when I get home from work. Still waiting on the pin drills to arrive.
                       
                    • SSG_Karg

                      SSG_Karg Heeeeeres Johnny!

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                      Pics

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