Holley/Demon Carb stumble

Mopar Racers Forum

  1. Cudafever

    Cudafever Well-Known Member

    Messages:
    4,106
    Likes Received:
    1426
    Joined:
    Sep 27, 2009
    Local Time:
    1:03 PM
    What it sounds like to me and i can feel it in the car, is a slight baug stumble, then its off to the races.
    The big fall on its face is not there anymore because i using PRH slower full throttle stomp.
    You can here the eng stumble for a fraction of a sec as the front end is all most at full travel. then it gone.
    Go back and watch from 3:10 to 3:19 focusing on 3:18 to 3:19 it fall flat then comes back on.
    That run shows it the best
     
  2. Cudafever

    Cudafever Well-Known Member

    Messages:
    4,106
    Likes Received:
    1426
    Joined:
    Sep 27, 2009
    Local Time:
    1:03 PM
    Also the Proform videos were from under the car. even in the slo mo start there is no pause then raise more.
    converter my be a bit tight, and i think it is but.........don't think it is the smoking gun.
     
    Last edited: Jun 1, 2020
  3. PRH

    PRH Well-Known Member

    Messages:
    2,029
    Likes Received:
    3077
    Joined:
    Dec 14, 2018
    Location:
    So. Burlington, Vt
    Local Time:
    3:03 PM
    I think you’d be able to see the “two stages” of stall on a video of the tac.

    Demon air bleeds don’t have numbers on them.
    If you don’t know what they are, you have to pin them to find out.
    I’m not sure how they’re sold nowadays, but they used to just come as a pkg of blanks that had a .017” pilot hole in them.

    That combo, that elevation....... that 850 Demon carb.
    That’s really not a very good match.
     
    • Like Like x 1
    • Agree Agree x 1
    • Cudafever

      Cudafever Well-Known Member

      Messages:
      4,106
      Likes Received:
      1426
      Joined:
      Sep 27, 2009
      Local Time:
      1:03 PM
      Agree
      Agree
      and Agree
      I think we agreed long a go this carb is just to big.
      #1 even on a bigger cubic eng, it's still not right.
      #2 it pulls all the way thru the rpm range(butt odometer)Better then the Proform.

      I don't have a good selection of pin bits.
      So this is the best i can do

      High Speeds .029-.030 (factory 31)
      Low Speeds .063-.077 (factory 70)
       
    • '63GT

      '63GT Well-Known Member

      Messages:
      1,024
      Likes Received:
      967
      Joined:
      Jun 9, 2018
      Location:
      Turlock, CA.
      Local Time:
      12:03 PM
      If you have a set of torch tip cleaners in your box, you may be able to narrow it down.. $(KGrHqMOKpwFIDgPmGqwBSINw6io!!__60_35.jpeg
       
    • Cudafever

      Cudafever Well-Known Member

      Messages:
      4,106
      Likes Received:
      1426
      Joined:
      Sep 27, 2009
      Local Time:
      1:03 PM
      I'm just laying all of this out into one post so it easier to find for right now.
      106_a11b56f375969effcef56d9f85df1588-jpg.jpg
      upload_2019-7-31_10-46-30-png.png
      upload_2019-8-1_8-9-40-png.png
      upload_2019-7-31_11-39-56-png.png upload_2019-7-31_11-43-17-png.png
      2_563dcfbef3f89ca8e6adc778fa357d6d.gif
       
      Last edited: Jun 2, 2020
      • Thanks! Thanks! x 1
      • PRH

        PRH Well-Known Member

        Messages:
        2,029
        Likes Received:
        3077
        Joined:
        Dec 14, 2018
        Location:
        So. Burlington, Vt
        Local Time:
        3:03 PM
      • Cudafever

        Cudafever Well-Known Member

        Messages:
        4,106
        Likes Received:
        1426
        Joined:
        Sep 27, 2009
        Local Time:
        1:03 PM
      • mderoy340

        mderoy340 Well-Known Member

        Messages:
        2,331
        Likes Received:
        1100
        Joined:
        Aug 2, 2012
        Location:
        Melbourne FL
        Local Time:
        3:03 PM
        The idle and main air bleeds in the demon are 8/32"x 1/8" you can buy brass set screws and drill your own. Smaller idle bleeds will fatten up the transfer slot mixture. I run .066 idle bleeds on my car at the track, .070 on the street. To lean on the idle circuit hurts the off idle transition. Next is the pump nozzle, do they immediately shoot fuel when the throttle is moved? If your running pink cams they are to slow. Try a blue cam up front if you have one.
         
        • Like Like x 1
        • PRH

          PRH Well-Known Member

          Messages:
          2,029
          Likes Received:
          3077
          Joined:
          Dec 14, 2018
          Location:
          So. Burlington, Vt
          Local Time:
          3:03 PM
          That’s still only 10 bucks ;)
           
          • Agree Agree x 1
          • PRH

            PRH Well-Known Member

            Messages:
            2,029
            Likes Received:
            3077
            Joined:
            Dec 14, 2018
            Location:
            So. Burlington, Vt
            Local Time:
            3:03 PM
            • Like Like x 1
            • PRH

              PRH Well-Known Member

              Messages:
              2,029
              Likes Received:
              3077
              Joined:
              Dec 14, 2018
              Location:
              So. Burlington, Vt
              Local Time:
              3:03 PM
              Demon Carburetion Air Bleeds 200082

              It would appear these now come with a .025” pilot hole now.
              Seems kind big.

              Not that you can use them, but the smallest Holley bleeds are available as small as .023”.

              I guess there’s always the solder option if you really need them smaller.

              I doubt this calibration would work at all on your combo, but the Mighty Demon 850 I was using as a dyno mule for motors in the 650-750hp range was:
              HSAB 26/26
              Jets 86/97

              I don’t have notes on the IAB, but I think it was only a few thou smaller than stock....... so like .066-ish.

              The fuel curve was pretty good, and it was pretty responsive on bigger cube motors.

              Once I settled in on that air bleed/jetting combo, I was able to leave it alone.

              4EEEBB3D-5E46-4456-A111-1A119AC04ACF.png
               
              Last edited: Jun 1, 2020
              • Like Like x 2
              • Cudafever

                Cudafever Well-Known Member

                Messages:
                4,106
                Likes Received:
                1426
                Joined:
                Sep 27, 2009
                Local Time:
                1:03 PM
                • Like Like x 1
                • j par

                  j par Well-hung Member

                  Messages:
                  22,860
                  Likes Received:
                  11488
                  Joined:
                  Jul 2, 2014
                  Location:
                  Portland Oregon
                  Local Time:
                  12:03 PM
                  Ordering more stuff? LOL I wonder if you could have had a EFI by now?... I guess that would have been a different education...:D...
                   
                • Cudafever

                  Cudafever Well-Known Member

                  Messages:
                  4,106
                  Likes Received:
                  1426
                  Joined:
                  Sep 27, 2009
                  Local Time:
                  1:03 PM
                  EFI U :p
                   
                  • Like Like x 2
                  • Cudafever

                    Cudafever Well-Known Member

                    Messages:
                    4,106
                    Likes Received:
                    1426
                    Joined:
                    Sep 27, 2009
                    Local Time:
                    1:03 PM
                    If i just wanted it to run decent.............i would have got a 3310 or 6777 off of ebay and been done with it. I'm greedy! I want more, and i want to learn more even if it cost me money (that I don't have right now). But $20 buck i can swing.
                     
                    • Like Like x 1
                    • Agree Agree x 1
                    • '63GT

                      '63GT Well-Known Member

                      Messages:
                      1,024
                      Likes Received:
                      967
                      Joined:
                      Jun 9, 2018
                      Location:
                      Turlock, CA.
                      Local Time:
                      12:03 PM
                      Great attitude!
                      Nothing came easy for me either. I was always too broke to be real effective, but did have invaluable help.
                      I had to improvise constantly, but the education was priceless! Stay motivated.
                       
                      • Thanks! Thanks! x 1
                      • Agree Agree x 1
                      • Cudafever

                        Cudafever Well-Known Member

                        Messages:
                        4,106
                        Likes Received:
                        1426
                        Joined:
                        Sep 27, 2009
                        Local Time:
                        1:03 PM
                        Found the thread with the metering blocks cutaway
                        Page 4
                        Power Valve Selection: The Definitive Answer

                        So i'm trying to get rid of the pore transaction with a smaller air bleed. Idle air bleed? just rears or all ?

                        I have a 6.5 Power Valve in and am thinking of going with a 10.5 that i have on hand.

                        So here is my question. do i plug the PV and find the flat spot?
                        Do i use vacuum gauge and set it just above my starting line launch rpm or do i watch the vacuum and put a power valve in just above whatever it stumbles at.???
                         
                      • yellow rose

                        yellow rose Doctor of Thinkology.

                        Messages:
                        22,067
                        Likes Received:
                        18132
                        Joined:
                        Jun 19, 2015
                        Location:
                        Living on the razors edge
                        Local Time:
                        12:03 PM
                        I’d start by measuring cruise vacuum. Then I’d check that against how much vacuum you pull at starting line RPM under load because you’re foot braking.

                        Don’t you have billet metering blocks? They won’t have porosity like those junkers (I didn’t look at the link you posted yet, but I suspect that it has pictures of a pair of metering blocks I cut away that Mattax was kind enough to post so everyone could see them...which is why I can call them junkers...because they are).

                        Any time you have a jet that meters air, going bigger will make the A/F ratio leaner. Any time you have a jet that meters fuel, going bigger will make the A/F ratio richer.

                        Which bleed you change makes a difference where the change will change the shape of the fuel curve. For example, if you change the main air bleed, you will make the fuel curve at WOT leaner, but you also delay the booster coming on. So if you want to lean out the end of the fuel curve, but you don’t want to delay the booster, you can change an emulsion jet to a larger one lower in the metering block.

                        Its stuff you have to test.
                         
                        • Agree Agree x 1
                        • Mattax

                          Mattax Just the facts, ma'am FABO Gold Member

                          Messages:
                          10,554
                          Likes Received:
                          6580
                          Joined:
                          Feb 7, 2013
                          Location:
                          Phila. Pa
                          Local Time:
                          3:03 PM
                          Trouble is IIRC that car never cruises on a highway. LOL :)
                          My sense is that its worth trying a higher opening power valve.
                          Reading post 651.
                          The engine goes flat? as the car launches.
                          Remind us, rpms are what at launch?
                          Load must be high as the car has risen. Would be interesting to see the vacuum but its got to be close to atmosphere as the throttle goes to the floor.
                          @mderoy340 may know and his car launches well.

                          The tricky thing with the air is going bigger with the bleed or upper e-hole is that it can actually move more fuel at the begining of flow.

                          In my experience, it has seemed to me when experimenting that even at slow idle, the idle air flow is already in he upper half of its maximum capacity.
                          I picture it like this. And at launch, if the idle circuit is contributing its got to be close to 100 % of what it can flow.
                          upload_2020-6-3_8-55-25.png

                          If the main circuit is in the start up of flow, then it could be a slighly larger MAB or top e-hole could get fuel delivery moving sooner (richer).
                          I just don't have a good picture of where the airflow is on the carb during a launch like yours.
                          106_a11b56f375969effcef56d9f85df1588-jpg-jpg.jpg

                          What I've always said, and try to do, is make changes to the Main Air Bleeds to adjust the fuel curve to be flat from mid rpms to redline in top gear (highest loads).
                          Then change e-bleeds if the begining if the transition or start up of the main circuit seems messed up.
                           
                          • Agree Agree x 1
                          • '63GT

                            '63GT Well-Known Member

                            Messages:
                            1,024
                            Likes Received:
                            967
                            Joined:
                            Jun 9, 2018
                            Location:
                            Turlock, CA.
                            Local Time:
                            12:03 PM
                            I agree to both..
                            The elephant in the room is the crazy elevation you're running in. IMO this will make it bleed sensitive.
                            Maybe if we had someone used to running in Denver conditions could elaborate? ( Off to work)
                             
                            • Like Like x 1
                            • Agree Agree x 1
                            • Cudafever

                              Cudafever Well-Known Member

                              Messages:
                              4,106
                              Likes Received:
                              1426
                              Joined:
                              Sep 27, 2009
                              Local Time:
                              1:03 PM
                              Every ono keeps saying change idle air bleed and i keep thinking why??? I need the mains to come on sooner........Got to quit thinking that way. The HSAB is for fuel trim not start of signal:BangHead:
                              Richer transfer slot is what i'm after and then trim it with the idle mixture screw....I think that's right????

                              Think i'm going to start with the power valve first.......Besides, i promised a video over the carb and 3 gear rolling stomp.
                               
                            • Mattax

                              Mattax Just the facts, ma'am FABO Gold Member

                              Messages:
                              10,554
                              Likes Received:
                              6580
                              Joined:
                              Feb 7, 2013
                              Location:
                              Phila. Pa
                              Local Time:
                              3:03 PM
                              I don't know if it needs richer t-slots or soon main circuit start up.
                              BUT.
                              A big change to the HSAB to change get the mains started earlier/stronger will affect the top of the curve.
                              Then how does that get fixed?

                              IF you want to experiment with idle circuit, a smaller IAB should make the idle richer. My experience has been it will affect slow idle mix too. Not always alot but noticible. Others may have different experience on that.
                              If the IFR is a little too small it will choke off the flow (max out) before the main circuit gets established.
                              Going to a slightler larger IFR and IAB is the way to keep the AFR about the same but extend its contribution into high air flow.

                              I'd don't know what I'd do in your shoes. Probably experiment with the upper e-holes first. See what the guys who have experience doing what your doing say.
                               
                            • Cudafever

                              Cudafever Well-Known Member

                              Messages:
                              4,106
                              Likes Received:
                              1426
                              Joined:
                              Sep 27, 2009
                              Local Time:
                              1:03 PM
                              One more question.
                              I cant get my pee brain around them scales
                              106_a11b56f375969effcef56d9f85df1588-jpg-jpg-jpg.jpg



                              Were or what is A and B and I mean, i get that m,o,n is different air bleed sizes and i get that X,Y,Z is the fuel ratio created by the venturi.
                              But Were is A B C D?
                               
                            • Mattax

                              Mattax Just the facts, ma'am FABO Gold Member

                              Messages:
                              10,554
                              Likes Received:
                              6580
                              Joined:
                              Feb 7, 2013
                              Location:
                              Phila. Pa
                              Local Time:
                              3:03 PM
                              I don't have that full page but its referenced the other way.
                              A and B are bleed locations in the well, what we usually call Emulsion-holes.
                              D is the air bleed

                              The small letters are references to the lines.
                              Line from o to z would be our goal.
                              Reducing the number of emulsion holes (might have been a tube type arrangement) resulted in late start as shown by dashed line n - b.
                               
                            1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
                              By continuing to use this site, you are consenting to our use of cookies.