Quick fuel carb fuel pressure too high? Rich idle...

Fuel and Air Systems

  1. Oldmanmopar

    Oldmanmopar Going left turning right FABO Gold Member

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    I was telling him some of the things to check for rich mixture ???? CLICK ON THE LINK.. Where did I just here that ?

    Holley Power Valve Tuning
     
    Last edited: Oct 22, 2020
  2. thesiren74

    thesiren74 Well-Known Member

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    Open the secondary idle screw.
     
  3. thesiren74

    thesiren74 Well-Known Member

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    I adjust mainly the secondary throttle plate screw to let more air in the engine and it helps a lot! Don't forget to readjust the accelerator pump arm after you turn that screw.
     
  4. mbaird

    mbaird mbaird

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    I have an 850 DP with anular boosters that I can send you for a test mule.
    If you like it but it and if not just send it back . I have some QF billet metering blocks and quick change float bowls on it but will send all the stock stuff as well.
    Worst that could happen is you Dyno t me a carb for me ...lol
    Would love to see the results !

    And I am in Boise so cheap shipping.
     
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    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

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      Yeah, I clicked on the link. That is the WRONG way to time power valve opening.

      Holley KNOWS at his, they just don’t want to admit they’ve been doing it wrong for decades and are STILL telling people to do it wrong.

      No wonder so many people want to junk their Holley carb. When the vast majority of tuners out there do something so wrong as setting PV timing off of half of idle vacuum it’s no wonder they hate them. It’s no wonder they get piss poor fuel mileage. It’s no wonder they need to run accelerator pump nozzles so big they move the fuel gauge every time you touch the throttle.

      FABO’s 12many went out and tested between the wrong way to time PV opening verses the right way to do it, and posted his results here. It should be made a sticky.

      No matter how many books are written, no matter how many dumbtube videos are produced, no matter how many times its repeated on forums, blogs, at dyno session, drag strips, bars, strip clubs, BBQ’s, Thanksgivings, Christmas, New Year’s Eve, bachelor parties or anywhere else two or more gearheads get together and the subject comes up it is still wrong to set PV timing from 1/2 of idle vacuum.

      Doing it that was is 180 degrees wrong from the way the PV operates. The PV has zero to do with or effect on the idle circuit.

      It’s that simple. That’s not how it works, that’s not what it’s for.

      You set PV timing 2-3 numbers LOWER than CRUISE vacuum and then you need to go back and unscrew all the wrong tuning done by timing the PV the wrong way.
       
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      • mbaird

        mbaird mbaird

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        I started tuning my Holley this way and it makes a positive difference. I still don't have it fully twerked but my AFR in the mid-range is much better.
        Some of my low speed issues may be due to can timing or such .
         
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        • mbaird

          mbaird mbaird

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          Tweekwd
           
        • mbaird

          mbaird mbaird

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          Tweeked.....
          I think my thumbs are getting fat !
           
        • yellow rose

          yellow rose Overnight Sensation FABO Gold Member

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          Tweaked, twerked...close enough for horse shoes and hand grenades!!!
           
        • cawcislo

          cawcislo Well-Known Member

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          ‘that’s a really great offer but for the time being I would have to decline. Winter has showed up early this year We just got about 10cm of snow here so messing with the idle is about all I can do until the spring, plus I want to setup a wideband to help get the tuning done faster.
           
        • cawcislo

          cawcislo Well-Known Member

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          Noticed my voltage was dropping And giving me Ignition problems last night as my Alternator doesn’t charge very well at 800 to 1000 rpm Probably should replace the alternator as I need 12 volts plus to run the distributor and coil properly before I continue. I think that upping the idle air bleeds would help. Yes stock look to be 70’s. Maybe I should go up 4 or 6 sizes to start?
           
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          Ok Guys. Here's the video Mark Whitener made opening an externally controlled power valve while the engine is idling.


          Here's the technical explanation why, in most cases, the power valve (or step up) has no appreciable effect on idle mixture.
          Motorsports Village • View topic - Power valve flow ????

          Are there exceptions? Yes. When the idle jet and/or PVCR is large relative to the normal relationship with the main jets. These are situations when opening the power valve (or raising the rods) can cause a significant change in the pressure in the main well which in turn causes an increase in flow into the idle well.
          See Shrinker's post 7 & 10 in the archived thread here:
          Power Valve Question
           
          Last edited: Oct 22, 2020
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          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Since this is your thread lets get back to the issues and I'll try to help.
            If you want to throw in a 10.5 PV, its not going to hurt. But I agree with YR and the others that's not the real issue.
            Possibility in order they should be looked at. None are neccessarily 'it' or more likely or less likely. Just that the sequence of getting the carb set up is important. One does effect the next
            1. Fuel Pressure. Lower is better. If you're using a regulator, set it at 4.5 psi and it will be able to flow more when more is needed and have less turbulence. That said, 6.5 psi should be controllable and if you didn't seethe fuel level creeping up in the sight plugs, it obviously was.
            2. Fuel Level. On the new school fuel bowls with big windows, fuel level should be in the middle of the windows. Set the secondaries sa little lower. On the older bowlswith smaller removable plugs, the typical starting point is fuel level just even with the bottom. Again lower on the secondaries. Setting the fuel level higher does make the mixtures richer. Not a lot but is an adjustment that can be used.
            3. Transfer slot settings. With the QF, start with the primaries square and the secondaries square or less than square. I'd be fine with no secondary slot showing but you may have to measure and experiment.
            4. Four corner. The elephant in the room. The idle-transfer systems work by the pressure difference between the bowl and the intake manifold. A four corner carb doubles the idle systems but does not double the air flow. It can be really useful with engines that have poor vacuum at idle.
            With a 4 corner on an engine with somewhat decent vacuum at idle, the fuel will probably need to be restricted much more.

            That should get you started.

            As far as the electric power goes.
            Even with the alternator dead there should be around 12 volts from the battery.
            Put that battery on a charger!!!
            Even a stock alternator could provide some power at idle - enough to run the ignition and field at close to 14 Volts and some left over to charge the battery if needed. So yea check into that AFTER getting the battery recharged.
             
            Last edited: Oct 22, 2020
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            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              yup. The half idle guidance goes back before video or even internet. Although in some books it says 1/2 crusing vacuum instead. That at least has a some relation to the purpose of enriching AFR as the engine approaching maximum acceleration or load.

              The only explanation I've seen for how we ended up with such a misunderstanding of the power valve selection is Tuner's. You're welcome to read it and decide for yourself whether it helps explain it, because
              (a) its his opinion based on his experience and observations and other people may have different experiences and observations
              (b) its more about how low PV numbers became popular with hot rodders and racers, drag racing in particular, and not directly about the half idle vacuum method of selection.
              See Post 57 in Power Valve Selection: The Definitive Answer
               
              Last edited: Oct 22, 2020
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              • dogbreath

                dogbreath Well-Known Member

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                Start with 76 IAB´s and work larger until you get a nice crisp snappy idle with mix screws between 1-2 turns out , of course assuming everthing listed above has already been done.
                 
              • yellow rose

                yellow rose Overnight Sensation FABO Gold Member

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                Can we take all those links about this stuff, put it in one post and make a sticky out of it? That would be much easier than typing it out on a regular basis.

                Just spitballing here. I have hope that that goofball tuning of the PV would eventually die off, but it never will as long as Holley continues to teach that.
                 
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                • Jeremiah

                  Jeremiah Well-Known Member

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                  I usually end up between 73-80 on the IABs.

                   
                • cawcislo

                  cawcislo Well-Known Member

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                  Battery put on a charger, New alternator ordered I’ll fire it up again tomorrow and see what I can do. Ordered some larger idle air bleeds also. I’ll check the fuel levels again and lower fuel pressure if need be and see what happens.
                   
                • cawcislo

                  cawcislo Well-Known Member

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                  Update.... finally got some time and weather to play with the carb. I pulled the carb, swapped in 78 air bleeds (stock 70), blasted some carb cleaner through the idle air bleed passages, even though the whole carb looks very clean inside and out. Swapped in another 6.5 power valve in case this one was acting up. Dropped the fuel level to 1/3 of the sight glass instead of 1/2. Tested this out, front mixture screws, still Had to be turned almost all the way in and when I did turn them all the way in The car didn’t stall so transfer slot must have been completely closed, I could turn the secondary Mixture screw in All the way and the car would die. Pulled the carb and closed up the secondary Butterfly to shut the transfer slots from just a hair over square to Just barely there. Fired it up again... so it’s idling way better, still shaky idle, and now I’ve got 1/2 turn out on secondary mixture screws and about 1 turn out on the fronts. Still can’t get idle less then 875 with the throttle screw all the way unscrewed so at this setup like primary transfer slot is completely closed (I checked when the carb was off).

                  initial timing is at 16 degrees btdc. I think my next step is to close up the secondary butterfly a bit more but that will reduce my secondary transfer slot to zero. Then I can open up my primary butterfly and hopefully get my idle to 800 rpm. I think I may need even bigger idle air bleeds as well probably like an 82. I wonder if the carb is originally intended for big cams with little vacuum at idle. I’m making between 15 and 16 vac At idle with my little 224 @ 0.050 cam. Let me know what you think.
                   
                • yellow rose

                  yellow rose Overnight Sensation FABO Gold Member

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                  It’s time to do 2 things. The first is find the Idle Feed Restricters and if they are at the top move them down. And then measure them and reduce the size by .004 and go from there.
                   
                • toolmanmike

                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                  This is for the other guys to answer but pay attention @cawcislo, does the floats adjust on this carb like the Holleys do? Shouldn't the fuel level be at the bottom of the bowl plug or site glass if you will an not a 1/3-1/2 way up?
                   
                • yellow rose

                  yellow rose Overnight Sensation FABO Gold Member

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                  If his carb has sight plugs, fuel should just drip out when jouncing the fender.

                  It it has a sight glass, 1/3 to 1/2 up from the bottom is where it should be.

                  I tend to shade it to the 1/3 level.
                   
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                  • toolmanmike

                    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                    Thanks for the clarification.
                    I have never worked with any of the new carbs just lots of the old Holleys. I remember someone, probably Mr. Gasket, made clear sight glass plugs. No reason for those if the fuel level is supposed to be at the bottom of the threaded holes.
                     
                  • cawcislo

                    cawcislo Well-Known Member

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                    The quick fuel I’m working with has the sight glass fuel bowls and generally they specify to run them at half way In the sight glass which some believe is too high of a fuel level. So I moved mine to 1/3
                     
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                    • cawcislo

                      cawcislo Well-Known Member

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                      thanks for the tip.

                      is the diagram below what you are recommending? I don’t have any spare idle feed restricters Perhaps I’ll start with just relocating them. Primary and secondary side or primary side only?

                      DD89F6BE-FB58-475D-A89F-2ACF224F9CB6.png
                       
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