Vacuum Question

Discussion in 'Fuel and Air Systems' started by RPMagoo, May 30, 2018.

  1. RPMagoo

    RPMagoo Just An Old Motorhead

    Messages:
    2,351
    Likes Received:
    842
    Joined:
    Nov 4, 2015
    Location:
    N.E. Pa.
    View My Photos
    Local Time:
    7:39 AM
    I have a early (66) 383 Mopar, pretty much stock, and just installed a Edelbrock 1406 carburetor. Timing set at 15 and 36 degrees. The motor had a flutter under slight acceleration between 1500 and 2200 RPM, with the vacuum hose connected to the "Timed Vacuum" port on the passenger side of the carb. -- I moved it to the "Manifold Vacuum" port on the driver side of the carb, and readjusted the idle, downward. I also moved the accelerator pump bracket from the middle hole to the hole nearest to the carb body (increased the squirt), and the flutter went away.. -- I moved the pump bracket 1st - slight improvement -- then switched the vacuum hose - presto, problem gone. -- Timing, vacuum, and carburetors are something that I am not very adept at, so please don't shoot Me. There are many different opinions regarding where to hook the vacuum to the carb. -- Have I done something wrong, and just got lucky -- or -- ???
     
    Last edited: May 30, 2018
  2. 72Dart6pack

    72Dart6pack Harder Better Faster Stronger.

    Messages:
    2,042
    Likes Received:
    1233
    Joined:
    Feb 1, 2016
    Location:
    Roseville Michigan
    Local Time:
    8:39 AM
    And did you call me first? No!
    :poke:
     
  3. 72Dart6pack

    72Dart6pack Harder Better Faster Stronger.

    Messages:
    2,042
    Likes Received:
    1233
    Joined:
    Feb 1, 2016
    Location:
    Roseville Michigan
    Local Time:
    8:39 AM
    I might know a thing or two on carbs. Just saying. Lol

    IMG_25071.jpg
     
  4. RPMagoo

    RPMagoo Just An Old Motorhead

    Messages:
    2,351
    Likes Received:
    842
    Joined:
    Nov 4, 2015
    Location:
    N.E. Pa.
    View My Photos
    Local Time:
    7:39 AM
    -- So - One more opinion. -- What's Your answer ?
     
  5. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

    Messages:
    2,535
    Likes Received:
    1075
    Joined:
    Feb 7, 2013
    Location:
    Phila. Pa
    Local Time:
    8:39 AM
    If its pretty much stock, then use the factory as baseline. They had figured out a thing or two about the timing curves.
    I don't have a '66 book but do have a '67. I can tell you the mechanical advance for the 2 bbl looks noticibly different than the 4 bbl.
    15* initial at 600 rpm would be about as much advance as would be wanted for a stock cam'd 383. So no, don't add manifold source for th evac advance on top of that.
     
    • Thanks! Thanks! x 1
    • Agree Agree x 1
    • RPMagoo

      RPMagoo Just An Old Motorhead

      Messages:
      2,351
      Likes Received:
      842
      Joined:
      Nov 4, 2015
      Location:
      N.E. Pa.
      View My Photos
      Local Time:
      7:39 AM
      -- I understand that , but, why did the stumble go away ? -- What's the danger ?
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

      Messages:
      2,535
      Likes Received:
      1075
      Joined:
      Feb 7, 2013
      Location:
      Phila. Pa
      Local Time:
      8:39 AM
      Not really sure what you did there with the carb adjustments, but the fact it needed more pump shot suggests you made it leaner. I'll guess that adding timing to the 15* at idle made it a better match for the mix. How much timing was added? 5*, 10*, 15*? No real danger, just less efficient burn in relation to pushing the piston down the hole with the most leverage.

      Its better to get the timing about right, and then adjust the carb. Even using the factory specs, there's some expected adjustment. Say its 10* at 600, well then 12 or 14* would still be in expected range. But 10 + 15* is well beyond the range. Yes it will run at 25*. And I don't know if its 15*, just throwing that out there as an example.

      Timing is about firing the mix so the burn develops maximum pressure at through the most efficient position of the piston. How long a mix takes to burn and develop pressure varies with combustion chamber, compression and heat, as welll rpm (hence the mechanical advance) and mixture (hence the vacuum advance).
       
      • Thanks! Thanks! x 1
      • RPMagoo

        RPMagoo Just An Old Motorhead

        Messages:
        2,351
        Likes Received:
        842
        Joined:
        Nov 4, 2015
        Location:
        N.E. Pa.
        View My Photos
        Local Time:
        7:39 AM
         
      • RPMagoo

        RPMagoo Just An Old Motorhead

        Messages:
        2,351
        Likes Received:
        842
        Joined:
        Nov 4, 2015
        Location:
        N.E. Pa.
        View My Photos
        Local Time:
        7:39 AM
        No adjustments to the carb, other than a slight adjustment to the 2 idle mixture screws - very near to the edelbrock settings. - Timing is set at 15* at 900 RPM, vac disconnected. -- (1) Does all that I've done explain why the stumble went away ? -- (2) Should I put the vacuum tube back onto the ported side of the carb and be considering some changes to the carb instead ? -- The car is a 3,000 lb Street Rod - Stock Convertor - Auto Trans - 3.54 gears. -- Runs fine, as is, up to 80+ MPH - tempted to leave it as is, but don't want to cause other problems.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

        Messages:
        2,535
        Likes Received:
        1075
        Joined:
        Feb 7, 2013
        Location:
        Phila. Pa
        Local Time:
        8:39 AM
        Not enough info to answer (1). It would be more guessing and speculation. Post #7 is as far as I'll go with that.
        As far as (2), in general yes, but again not enough info. See post #5.
        The following gives us the possiblility of 2 or 3 engine configurations.
        and this suggests it may be none of the above.
        To know the curve we need the RPMs and at least a few in between points. If its the original distributor that came with the engine, the specs are in the shop manual - so that can be estimated. But most guys who street rod put something else in. So who knows.

        Changed too many things to guess what effected what. Very light acceleration should be fueled by the "idle circuit" which includes the transfer port. Pump shot helps cover the delay when the throttle is moved quickly while on the "idle circuit".

        Who ya kidden? :poke: LOL
        You adjusted the base idle mix. "a slight adjustment to the 2 idle mixture screws"
        Maybe did something with the thottle position "and readjusted the idle, downward"
        Changed the pump shot twice "moved the accelerator pump bracket from the middle hole to the hole nearest to the carb body"

        Why is it idling at 900 rpm with a stock engine?

        Can't tell whether you're interested in tuning, or just happy with it the way it is. If you're happy, enjoy. If you enjoy tuning, then keep working on it.
         
        • Agree Agree x 1
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

          Messages:
          2,535
          Likes Received:
          1075
          Joined:
          Feb 7, 2013
          Location:
          Phila. Pa
          Local Time:
          8:39 AM
          • Like Like x 1
          • Thanks! Thanks! x 1
          • RPMagoo

            RPMagoo Just An Old Motorhead

            Messages:
            2,351
            Likes Received:
            842
            Joined:
            Nov 4, 2015
            Location:
            N.E. Pa.
            View My Photos
            Local Time:
            7:39 AM
          • j par

            j par Well-hung Member

            Messages:
            7,942
            Likes Received:
            2267
            Joined:
            Jul 2, 2014
            Location:
            Portland Oregon
            View My Photos
            Local Time:
            5:39 AM
            Because you have three Hollyz you know how to adjust his Edelbrock?
             
          • j par

            j par Well-hung Member

            Messages:
            7,942
            Likes Received:
            2267
            Joined:
            Jul 2, 2014
            Location:
            Portland Oregon
            View My Photos
            Local Time:
            5:39 AM
            Is the carb brand new?
             
          • RPMagoo

            RPMagoo Just An Old Motorhead

            Messages:
            2,351
            Likes Received:
            842
            Joined:
            Nov 4, 2015
            Location:
            N.E. Pa.
            View My Photos
            Local Time:
            7:39 AM
            -- Yes.
             
          • j par

            j par Well-hung Member

            Messages:
            7,942
            Likes Received:
            2267
            Joined:
            Jul 2, 2014
            Location:
            Portland Oregon
            View My Photos
            Local Time:
            5:39 AM
            Changing the position on the accelerator pump arm usually is something that's done to an older carburetor to get it to function better. I had several stumbles and things due to the wrong size Jets and definitely due to not having strong enough Springs in the metering rods. The right weight spring and metering Rod helps a lot especially if they're is a performance cam or something in it.
            You could have had a blocked passage or bad gas or something? But the accelerator pump is basically just for tip in. Not at the 1500- 2200 RPM Mark where you're talkin. Possibly in lieu of needing a bigger jet or smaller metering rod you're over use of the accelerator pump maybe a making up the difference?
             
            • Thanks! Thanks! x 1
            • RPMagoo

              RPMagoo Just An Old Motorhead

              Messages:
              2,351
              Likes Received:
              842
              Joined:
              Nov 4, 2015
              Location:
              N.E. Pa.
              View My Photos
              Local Time:
              7:39 AM
              -- I talked to Edelbrock Tec., and they said to switch to pink springs - currently yellow. -- I ordered a spring kit from Summit.
               
            • j par

              j par Well-hung Member

              Messages:
              7,942
              Likes Received:
              2267
              Joined:
              Jul 2, 2014
              Location:
              Portland Oregon
              View My Photos
              Local Time:
              5:39 AM
              Your local parts store should have a spring set for like 8 bucks..
               
            • RPMagoo

              RPMagoo Just An Old Motorhead

              Messages:
              2,351
              Likes Received:
              842
              Joined:
              Nov 4, 2015
              Location:
              N.E. Pa.
              View My Photos
              Local Time:
              7:39 AM
              -- None around here. I checked them all. -- I'm in The Boonies.
               
              • Like Like x 1
              • j par

                j par Well-hung Member

                Messages:
                7,942
                Likes Received:
                2267
                Joined:
                Jul 2, 2014
                Location:
                Portland Oregon
                View My Photos
                Local Time:
                5:39 AM
                I like the boonies! LOL Yeah our local Baxter's usually has quite a nice selection of jets metering rods and definitely that spring set.
                 
              • AJ/FormS

                AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

                Messages:
                12,764
                Likes Received:
                2740
                Joined:
                Jan 19, 2014
                Location:
                Southern Manitoba,Canada, 900ftelevation
                View My Photos
                Local Time:
                7:39 AM
                Depends on your Vcan, and when the 36 was in by; but I'm pretty sure the engine didn't like the total timing it was seeing, and you may have interpreted detonation as flutter.
                For instance if the centrifugal begins advancing at 1000 and is all in by 2800, then it is advancing 21* in 1800 rpm, or 1.67degrees per 100rpm. Therefore at 1500, she would be seeing 15* plus 5x1.67 plus the can which could be as little as 9 or as much as 22. So that totals 32* to 45*at light throttle. By 2200 it looks like 15* plus 12x1.67 plus 9 to 22= 44* to 57*, at light throttle.
                These numbers are probably too high for a stock iron headed engine

                Bottom line is this; if you can change the severity of the flutter by changing the amount of throttle, or if it disappears with a defeated Vcan....... then the flutter was probably detonation.
                And you want to avoid detonation at any cost, cuz detonation can break your pistons pretty quick.

                It seems there are some guys here on FABO, that are Gung-Ho to throw timing at every engine they come across. EDIT;In your case, this might be a prime example of what not to do.
                ______________________________________
                The factory timings on a 69 383-2bbl automatic,The only FSM I have, were pretty aggressive. I see it at; 7.5 initial, and 2 to 12 at 1000,16 to 20 at 1500,34 to 38 at 4600, and with 21 to 27 in the Vcan by 13.5 inches vacuum. The 4bbl specs are a bit tamer
                IMO, IMO,IMO, it is better to be 3 to 5 degrees retarded at all points, even 3 short at WOT, than even just 1 too many. On the street, at WOT, I can almost guarantee you,that your butt-dyno will not be able to measure perhaps even 3 degrees short of optimum.
                So, again, IMO, don't be in a hurry to throw timing at it, a mistake can be very expensive. Sneak up on it.
                _______________________________
                EDIT; I only tune SBMs, and only for street.
                I'm not against throwing timing at some combos, cuz it can and does work.
                SBMs,with automatics and hi-stalls,almost anything goes.
                But I have come across many cases of stock type engines when throwing timing at it doesn't work.
                And street engines, with manual transmissions is a special case, requiring discretion.
                But you need to keep in mind too, that a lot of initial timing,tames the lope in the cam, and everybody wants to hear the lope.
                So if you had a hi-compression360 with a stick, and a 270 cam, and you throw 22* into it at idle.......your precious lope will be as good as gone. And the carb tune you put into it, with a poor-choice of gears, will tend to make it very jumpy at low rpms, and parading it will be impossible. Whereas with an automatic, most of that jumpiness will be absorbed by the fluid coupling.
                But if you were to back the timing down to 5*, you would hear that lope pretty good. And the jumpiness would be pretty much gone. This is because your peak cylinder pressure will occur when the piston is much further down the bore, and the strength of that pulse will be much reduced.
                Of course, 5* is pretty lazy, but that's sometimes what it takes, especially for a VERY-high compression stick car with hiway gears, and he wants to parade it (me).
                The trick then, is to bring the advance curve in hard and fast to play catch up by mid 2000, and still hit the power-timing by the early to mid 3000s. And take care of the Part Throttle timing with the Vcan., to make up the difference.
                Without computer controlled timing, it is impossible to hit all the marks, so compromise is always tempering the choices. In a stick-car;I tend to sacrifice all power-timing below about 2000rpm, to favor part-throttle response. I also tend to sacrifice initial timing for PT response. Cuz face it; probably 95% of the engines life is spent in PT operation. I don't care about idle-lope, and with a hi-C 360 my butt-dyno cannot tell if the power timing is 3* short of what the engine dyno says is perfect. My tunes rely heavily on the Vcan.
                But I can sure tell if the engine is;lazy or jumpy, or Snapppppy.
                 
                Last edited: Jun 1, 2018
                • Thanks! Thanks! x 1
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

                  Messages:
                  2,535
                  Likes Received:
                  1075
                  Joined:
                  Feb 7, 2013
                  Location:
                  Phila. Pa
                  Local Time:
                  8:39 AM
                  All true A/J.
                  But here's the thing with those '69 specs, they're for a CAP engines, that's why there is a very fast primary curve. All CAP/CAS curves look like that when compared to their non CAP counterparts. The CAP engines used much less initial and then above idle the mechanical advance quickly made up for this. (There's other threads on this, so if you want to discuss, lets take it to one of them).
                  Without knowing the info requested in post #11, we're just throwing examples out that may or may not be directly applicable. (The principles you state are totally valid - so there's no arguement about that.)
                   
                • AJ/FormS

                  AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

                  Messages:
                  12,764
                  Likes Received:
                  2740
                  Joined:
                  Jan 19, 2014
                  Location:
                  Southern Manitoba,Canada, 900ftelevation
                  View My Photos
                  Local Time:
                  7:39 AM
                  Oh chit; I put this sentence in the wrong spot;
                  It applies to the OPs possible curve, not to the factory's.
                  I'll go edit

                  thx Mattax
                   
                • RPMagoo

                  RPMagoo Just An Old Motorhead

                  Messages:
                  2,351
                  Likes Received:
                  842
                  Joined:
                  Nov 4, 2015
                  Location:
                  N.E. Pa.
                  View My Photos
                  Local Time:
                  7:39 AM
                  -- Got them -- put them in -- Vac tube on the passenger side, of carb -- didn't mess with the timing -- runs smooth. -- Thanks to All, for Your input.
                   
                  • Like Like x 1
                  • racerhog

                    racerhog RacerHog likes his Mopars

                    Messages:
                    977
                    Likes Received:
                    214
                    Joined:
                    Nov 18, 2008
                    Location:
                    Monrovia SO-CAL
                    Local Time:
                    5:39 AM
                    Sounds like it just needed a little more fuel in the transfer.... Glad it feels better...
                    Lucky the car is light and not heavy, so its a little more forgiving...
                    Now.... Go burn some rubber !!!!!! And tell us how it really runs..... :)
                     
                    • Like Like x 1