Pulsing vacuum?

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  • blizzard
    #1

    Pulsing vacuum?

    I was working on my 78 GS1000E with the gas tank off and using my temporary tank. I had the vacuum line for the fuel petcock plugged. While I had the bike running I removed the vacuum line plug and put my finger over the line and noticed that I do not have a constant vacuum, it PULSES. I was going to sync the carbs soon and I don't know if I will be able to with this erratic vacuum? I actually removed one of the intake plugs that you tap into to sync the carbs and I have the same thing there also.
    Is this a problem, I would think it would give me problems when trying to sync carbs?
    The bike is running pretty good now after readjusting valves and rebuilding carbs, better than it has any time before.
    Thank you for any suggestions.
    Tags: None
    • atchbo
      #2
      I'm pretty sure the vacuum is just created by the piston moving down and valve opening... no getting around the pulsing.

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        • blizzard
          #3
          Are you saying that the pulsing is normal?

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            • Nessism
              Forum LongTimer
              GSResource Superstar
              Past Site Supporter
              Super Site Supporter
              • Mar 2006
              • 35790
              • Torrance, CA
              #4
              Of course vacuum pulsing is normal. Haven't you ever synced your carbs? The vacuum columns move up and down with each pressure pulse.
              Ed

              To measure is to know.

              Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

              Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

              Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

              KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

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                • blizzard
                  #5
                  Originally posted by Nessism
                  Of course vacuum pulsing is normal. Haven't you ever synced your carbs? The vacuum columns move up and down with each pressure pulse.
                  Actually I have not ever synced carbs before. I am used to working on multi cylinder automotive motors but I guess they are working on a single combined intake and there would not be a pulsing with all cylinders pulling through the same intake it would be smoother vacuum. I forgot I am only dealing with one cylinder vacuum at a time there would have to be a pulse, Duhh!
                  Sorry about the stupid question, next time I will try to think about it more closely.

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                    • Don-lo
                      #6
                      Most gauges have inline restrictors that smooth out those pulses. You'll be able to see when they are matched.

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                        • drhach
                          #7
                          Actually you can make a damper that will remove some or all of that. I took a 2 foot long 2" PVC tube and capped both ends. You put it inline with your gauge and it will remove flatten out some of that pesky oscillation.

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                            • Macmatic
                              #8
                              Is it normal to feel that same pulsation in the fuel line or is that a sign of something going wrong with the petcock?

                              /\/\ac

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                                • Guest
                                  #9
                                  It's called compression.

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