Holley/Demon Carb stumble

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  1. Andrezinho

    Andrezinho FABO Gold Member FABO Gold Member

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    Good morning all,
    I allow myself to give you an advice, very modest that my 35 years of experience in motors give me.
    when you go to work on your: carburetor, ignition, valve adjustment, ... make notes in a notebook, it's really very important.
    always only one change at a time,
    each setting change must give a positive result, no change? be careful!
    for the lambda probe, very important the location !!!
    the choice of the location of the lambda probe must be to respect this operating temperature.
    once again I apologize for my english. I only wanted to advise you to do the most meticulous work, and always with notes.
    another very important point in my modest opinion:
    always look for the real truth of the engine !! and not imagine in your head.
    and always new spark plugs.
    good race
     
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    • Cudafever

      Cudafever Well-Known Member

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      at 2.13 minutes into the video i changed from the proform to the demon.
      If i roll the throttle in i can get the demon to launch. and is what you are seeing the last several launches.
      no timed runs, no track prep.
      Going to get a few ets on both carb, Then this thread will be done i think.

      Lost my job and theres no money to do or try anything from this point on, for a while. selling house, moving and trying to find a new job is all not going to be fun..................Any ways whining off.

      The seat of the pants says Proform idles and 60 foots much better.........Demon still stumble if i tromp on it to fast and the idle is not as clean. However my butt odometer says the Demon still pulls harder on the top end.
      Going to need some et slip to answer these questions.
      stay tune......
       
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      • '63GT

        '63GT Well-Known Member

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        Interesting...
        Curious, are the bleeds the same, carb to carb?
         
      • Cudafever

        Cudafever Well-Known Member

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        The hole tune/calibration is different top to bottom between the tw0 carbs.
        I really wanted to start to do and learn how to affect my tune with air bleed and tune the top end in and all. And i have a box of air bleed for the low, and the high bleed(for the proform) but i need a data logging o2 to even start down that road.
        No money for that right now........so i will just have to be happy with one of these carbs for now..........................

        The air bleed on the Demon are Half the size(thread side)compared to the standard holley/proform main body.
         
      • '63GT

        '63GT Well-Known Member

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        I understand.
        I don't wish to undermine anyone else's suggestions..
        Just a thought, beings the specific gravity of fuel doesn't change with altitude (sarcasm) but air does (you're at 9000ft right?)
        I'm wondering if your issue couldn't be resolved just by simply reducing the low bleed by a couple sizes, in an attempt to 'bring in' the fuel at the booster sooner? It might be worth trying if you have some on hand, even if it is to prove this wrong.
        just a thought, don't kill the messenger..
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        WOW that sucks about your job. I hope this isn’t because of the flu? Let’s hope you find something and get on with it. I hate that this happened to you.

        YR
         
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        • PRH

          PRH Well-Known Member

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          X2
           
        • PRH

          PRH Well-Known Member

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          Here’s my perception of what’s going on in the video.......
          The motor doesn’t really sound “sharp” with either carb.
          Basically, it comes across to me as a combo of...... cam is too big/CR is too low/not enough stall(no where near enough stall for a bracket car imo)..... probably mostly elevation related.
          What’s the track elevation there?
           
        • '63GT

          '63GT Well-Known Member

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          I think he said his average DA is hovering around 9000'
           
        • Cudafever

          Cudafever Well-Known Member

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          No messenger killing here.:elmer::lol: I appreciate all appinions
          First i have air bleed but only for the proform/holley. The Demon carb has much smaller brass inserts. found a small enough screwdriver to remove the air jet.
          With my reading glasses and a Magnifying glass I couldn't read any numbers on it and it look like it had a letter on it. Don't know but i don't have any air bleed for the demon except whats already in there.

          Maybe i could find some fine small wire and put that in there for temp to see.........bend a Z so it can't fall in.............
          When you say the low bleed your taking about the ones in the main body right?.....High Speed bleed? still learning.
           
        • Cudafever

          Cudafever Well-Known Member

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          YUP!!!
          Worked for a gas compression company for the past 8-1/2 year. made it thru the last gas and oil crisis. But the Damm CORONAVIRUS TOOK ME DOWN. I could go on a rant!!!!!:mob: ...... about all of this, but looking back just don't do anybody any good.
           
        • Cudafever

          Cudafever Well-Known Member

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          Here’s my perception of what’s going on in the video.......
          The motor doesn’t really sound “sharp” with either carb.
          Basically, it comes across to me as a combo of...... cam is too big 408 stroker, Hyd roller.562/.550, 243/247@ .050(@.006" 294/297 duration. Lob Lobe Separation @106 and i degreed it in at 101/CR is too low 12.87:1/not enough stall 4200 stall(nowhere near enough stall for a bracket car imo)..... probably mostly elevation related.6600' elevation, adjusted is anywhere between 7200 and 10,000 foot.
          Most of the time it's 8 to 9 Thousand foot adj altitude

          What’s the track elevation there?
          I shift at 5800 rpm

          I not arguing any of your point but adding answers to the questions.
          Where
          do you think my weakest line is?
           
        • '63GT

          '63GT Well-Known Member

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          Yes, closest to the nozzels are the HSB (high speed bleeds) and the outers are the LSB (Low speed bleeds or idle bleed as some like to call them)
          Just verify they're 31/70
          I went all the way back to your post #29, and spent a lot of time with the pause button..
          It looks like the only fuel it's getting is with the pump shot. I don't see much of any pull (fuel pull) in the boosters. Video is not ideal. I would like to see the same only in 3rd gear against the converter (short raps like you did) to see booster activity.
          This confirms my suspicion your low bleeds may be incorrect.
          Skrews provided a nice chart in post #30 to show what the carb should be set up with.

          To re-iterate, I suspect your carb may need different bleeds with the Density Altitude you're running in.
           
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          • '63GT

            '63GT Well-Known Member

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            p156611_image_large.jpg
             
          • Cudafever

            Cudafever Well-Known Member

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            Thank you for all of that.
            Why do you say idle bleeds need to be smaller?
            I don't understand how that helps.
            I will go back and re read that post and try to get my head around all of this again.

            In my mind, closing off the idle bleed wont bring on the venturis any sooner, or pull sooner. Closing of the air bleeds or reducing the the size of the High Speed air bleed would,.......Right?

            I'm wondering if your issue couldn't be resolved just by simply reducing the low bleed by a couple sizes, in an attempt to 'bring in' the fuel at the booster sooner?

            Going back to study back up a little....................

            As far as the gopro on top of the carb.........i might get time to do that this week.
             
            Last edited: Jun 1, 2020
          • PRH

            PRH Well-Known Member

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            Maybe I’m just hearing it differently than what’s actually happening....... but it sure doesn’t “sound” like it’s flashing to 4200.
            I’d like to see some gopro footage of the tac while you’re doing the high gear rolling flash stall test.

            Honestly....... the launch sounds to me like a mild street car with a typical 10” street/strip converter that’s stalling in the mid-3000’s.

            But....... that might just be how it comes across watching it on my phone.

            What are the 60’ times again?

            What’s the cranking compression look like?
             
          • Cudafever

            Cudafever Well-Known Member

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            I will add that to my gopro video.
             
          • PRH

            PRH Well-Known Member

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            I’d like to see what the tac is doing on a couple of runs too.

            How high do you load the motor before launching?

            My gut feeling is the long seat timing of the hyd cam is having a pretty noticeable impact on low speed grunt with that 6600’ elevation.

            I bet at a track under 1000-1200’ or so, it would seem like a totally different car.
             
            Last edited: Jun 1, 2020
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            • Cudafever

              Cudafever Well-Known Member

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              Here is a picture to show just how much smaller the idle and main bleeds are Demon carb
              img_1534-jpg.jpg
               
            • Cudafever

              Cudafever Well-Known Member

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              With the the old 3000 stall i was staging at 2200
              With the 4200 stall i now leave at round 1500 RPM
               
            • '63GT

              '63GT Well-Known Member

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              What are the bleed sizes?
               
            • PRH

              PRH Well-Known Member

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              Watched it again.........

              What it seems like is, it’s like there are two stages of stall.
              You floor it, the car drives off the line at something less than 4200, then the motor gets a little burst, and goes to what sounds like about 4200.

              But, what you want is to have the motor instantly jump to the 4200..... right at the hit.
              It doesn’t sound like that’s happening on the video.
               
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              • '63GT

                '63GT Well-Known Member

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                Yes! Major transition problem
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                I honestly can’t hear it well enough in the video. I need some better ear buds because the ones I have suck buttermilk.

                I have no doubt what you are hearing, and usually that means the converter is too tight.

                We just did a 5k 8inch PTC for a street drive truck. He had some unknown 10 inch (IIRC) 3500 deal in it before and the 8 inch drove better around town than the 10 inch and the 5k stall made it move.

                I’m going to listen again and see if I can catch it. May not be the ear buds. I’m better than half deaf.
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                Well...I think you may be right PRH. I just don’t trust my hearing on this video stuff, but looking very close and listening as best I can, it does look like on at least some of the hits it is slow off the throttle and then it changes tone and starts to RPM faster. It’s like the converter is tight enough it’s too far below peak torque and it takes a second (figuratively speaking) to get back up to and on the high side of peak torque.

                I hate being deaf.
                BTW, great video but I forgot to mention you could have given the dog a bit more face time on there. Dogs ALWAYS make a video better, and that dog is a cutie, nd yes I said cutie because I love dogs.
                 
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