Vacumn advance can adjustment screw, info please.

Electrical and Ignition

  1. 340doc

    340doc Well-Known Member

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    From what I've heard it doesn't change the amount of advance, just the rate. Is this so? Also which direction of adjustment does what? Thanks.
     
  2. toolmanmike

    toolmanmike FABO Staff Staff Member FABO Gold Member

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    • 340doc

      340doc Well-Known Member

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    • Murray

      Murray FABO Gold Member FABO Gold Member

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      The inside allen screw adjustment changes the rate of advance, or how sensitive the diaphragm responds to the vacuum. Been a long time, but I think if you turn the screw in or clockwise, it reacts faster, is more sensitive, advances sooner. The reverse would happen in the counter-clockwise direction. Someone can correct me if I got that wrong.
       
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      • Dana67Dart

        Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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        The rate is set by the spring rate and the total advance is set by the stroke. The pre-load or lack there of just sets the amount of vacuum it takes to start moving the diaphragm. The screw only adjusts the pre-load

        I have had some ford vacuum advance cans that you could screw off the end and replace the spring and the stop thus adjusting the rate and the total amount, pre-load was set with a spacer under the spring.
         
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        • 340doc

          340doc Well-Known Member

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          The advance seems to come in real quick on our 70 slant, causing it to ping. I watched it with a light. I'm hoping it has some adjustment available counter clockwise to slow it down a bit. Appreciate all your comments.
           
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          • Murray

            Murray FABO Gold Member FABO Gold Member

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            Just a heads-up. Not all vacuum advances are adjustable.
             
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            • 340doc

              340doc Well-Known Member

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              Thanks, I'm aware.
               
            • halifaxhops

              halifaxhops It's going to get stupid around here! FABO Gold Member

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              Look at the number on the arm also you might have a high one that was changed at some point. Know the distrib number I can look it up.
               
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              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                Single point or electronics are "usually" adjustable. Most dual points are not.
                 
              • halifaxhops

                halifaxhops It's going to get stupid around here! FABO Gold Member

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                If a 3/32 allen fits in it is adjustable. Mike you can do the older dual points with springs and shims silly!
                 
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                • Murray

                  Murray FABO Gold Member FABO Gold Member

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                  Another issue- the new repo BB vacuum advances do not indicate the amount of advance. My original on a 383 indicates "10.5" which is higher than most. Am reluctant to purchase these because of that. What do you boys think?
                   
                • toolmanmike

                  toolmanmike FABO Staff Staff Member FABO Gold Member

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                  I knew that but what a pain compared to a Allen wrench. LOL
                   
                • 340doc

                  340doc Well-Known Member

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                  Thanks, if adjusting it doesn't help me I'll pull the dist and get the number. I do recall seeing a tag on it.
                   
                • halifaxhops

                  halifaxhops It's going to get stupid around here! FABO Gold Member

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                  Probably a remanufactured unit then, one of the problems with them they set a curve so it works on a lot of applications, some good some bad. Never come with a number for obvious reasons.
                   
                • AJ/FormS

                  AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                  You can figure the number out real easy, just set it loose, install it, evacuate the chamber and read the timing change. Badabing.
                  If you screw it in until it is really,really slow, on mine, it began to limit the amount.
                  You can modify the total by filing the stops. I run as much as possible because she needs the timing at cruise rpm to make the gas-mileage.
                  A slanty pinging? How much initial? What elevation are you at? What stall and gears?
                  Have you tried Trading away some initial, then bringing the mechanical in faster to compensate.
                  I guess you've tried the usual stuff like intake air temp,AFR, and exhaust.. And solid lifter cams are a little sensitive to the hot-lash. Mine runs pretty good at 013/023 Hot. Not so good at the spec .010/.020.......
                  HappyHotrodding
                   
                  Last edited: Nov 6, 2018
                • 340doc

                  340doc Well-Known Member

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                  I'm at 6 initial. All stock slant. 3.23 gear. 12 and 22 on the valves. I'm pretty much at sea level. This all seemed to start when I swapped over to electronic. I really need to investigate the used dist. to see where everything's at, starting with the V-can. Appreciate your input.
                   
                • halifaxhops

                  halifaxhops It's going to get stupid around here! FABO Gold Member

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                  If it was a rebuild from the poarts store it can be anywhere. They are made to fit a whole span of years and applicationws.
                   
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                  • pishta

                    pishta I know I'm right....

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                    you can swap out the can, its 2 screws and a optional clip.
                     
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                    • SpeedyEd

                      SpeedyEd Member

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                      If you can't use the old vac. advance, try the Crane 99619-1 vac timing limiting plate. It was made for the Delco dist. but it should fit. I have a rebuilt vac unit that was rebuilt but the diaphragm wouldn't seal. But I can't locate it to verify the fit.
                      You could make a stop held by the mounting screw to limit the travel of the plunger.
                      SpeedyEd
                       
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