Vacuum vs gravity

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  • littleroot
    • Jan 2026
    #1

    Vacuum vs gravity

    For 80GS1100E

    Help me understand why Tom put a non-vacuum petcock on this bike. It is a nice new petcock. If there is some performance benefit I might leave it on but it not, Id rather not have to remmeber to turn the petcock off everytime I stop.

    Thanks guys for any advice.

    -Bob
    Tags: None
    • Dogma
      Forum Guru
      • Sep 2007
      • 7143
      • Mason, OH (SW)
      #2
      Some people don't trust the vacuum petcock, or get fed up with them after a rebuild fails.

      I'm like you: I trust a new vacuum petcock more than I trust myself to remember to turn off a manual one.
      Dogma
      --
      O LORD, be gracious to me; heal me, for I have sinned against you! - David

      Skeptical scrutiny is the means, in both science and religion, by which deep insights can be winnowed from deep nonsense. - Carl Sagan
      --
       '80 GS850 GLT
      '80 GS1000 GT
      '01 ZRX1200R

      How to get a "What's New" feed without the Vortex, and without permanently quitting the Vortex

        Comment

        • Big T
          Forum LongTimer
          Past Site Supporter
          Super Site Supporter
          • Mar 2005
          • 12391
          • West Slope, OR
          #3
          He probably hated the 1980 no handle petcock
          1978 GS 1000 (since new)
          1979 GS 1000 (The Fridge, superbike replica project)
          1978 GS 1000 (parts)
          1981 GS 850 (anyone want a project?)
          1981 GPZ 550 (backroad screamer)
          1970 450 Mk IIID (THUMP!)
          2007 DRz 400S
          1999 ATK 490ES
          1994 DR 350SES

            Comment

            • Steve
              GS Whisperer
              • Jun 2005
              • 35924
              • southwest oHIo
              #4
              I also prefer a vacuum-operated petcock, but I am wondering where "gravity" figures in your thread title.

              .
              sigpic
              mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
              hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
              #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
              #2 son: 1980 GS1000G
              Family Portrait
              Siblings and Spouses
              Mom's first ride
              Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
              (Click on my username in the upper-left corner for e-mail info.)

                Comment

                • Agemax
                  Forum Guru
                  • Apr 2008
                  • 8371
                  • plymouth uk
                  #5
                  Originally posted by Steve
                  I also prefer a vacuum-operated petcock, but I am wondering where "gravity" figures in your thread title.

                  .
                  because a vacuum tap is a vacuum operated gravity feed, where as a non vacuum tap is a manualy operated gravity feed tap
                  1978 GS1085.

                  Just remember, an opinion without 3.14 is just an onion!

                    Comment

                    • Steve
                      GS Whisperer
                      • Jun 2005
                      • 35924
                      • southwest oHIo
                      #6
                      Originally posted by Agemax
                      because a vacuum tap is a vacuum operated gravity feed, where as a non vacuum tap is a manualy operated gravity feed tap
                      Yes, but the title says "vacuum vs gravity", as if one were gravity-activated and the other were vacuum-activated.

                      Or maybe that one was gravity powered and the other was vacuum powered.

                      Following your suggestion, the title should have been "vacuum vs manual".

                      .
                      sigpic
                      mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
                      hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
                      #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
                      #2 son: 1980 GS1000G
                      Family Portrait
                      Siblings and Spouses
                      Mom's first ride
                      Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
                      (Click on my username in the upper-left corner for e-mail info.)

                        Comment

                        • Agemax
                          Forum Guru
                          • Apr 2008
                          • 8371
                          • plymouth uk
                          #7
                          i think we all knew what he meant!
                          1978 GS1085.

                          Just remember, an opinion without 3.14 is just an onion!

                            Comment

                            • Steve
                              GS Whisperer
                              • Jun 2005
                              • 35924
                              • southwest oHIo
                              #8
                              Originally posted by Agemax
                              i think we all knew what he meant!
                              Is that going to mean we can't have any fun with it?

                              .
                              sigpic
                              mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
                              hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
                              #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
                              #2 son: 1980 GS1000G
                              Family Portrait
                              Siblings and Spouses
                              Mom's first ride
                              Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
                              (Click on my username in the upper-left corner for e-mail info.)

                                Comment

                                • Agemax
                                  Forum Guru
                                  • Apr 2008
                                  • 8371
                                  • plymouth uk
                                  #9
                                  Originally posted by Steve
                                  Is that going to mean we can't have any fun with it?

                                  .
                                  of course not haha,
                                  1978 GS1085.

                                  Just remember, an opinion without 3.14 is just an onion!

                                    Comment

                                    • gearhead13
                                      #10
                                      I put a dual outlet Pingel on my bike to feed my RS38's I was told I needed one so that the bike wouldnt starve for fuel and lean out.
                                      It is hard to remember to turn it off, I lost a full tank of gas on the ground one time
                                      The fuel needles on the carbs only seal well when they want to. It drained out the overflows onto the ground.

                                        Comment

                                        • Guest
                                          #11
                                          Originally posted by Steve
                                          Is that going to mean we can't have any fun with it?

                                          .




                                          I like the no hassle of the vacuum operated one.
                                          Last edited by Guest; 04-02-2013, 08:11 PM.

                                            Comment

                                            • Guest
                                              #12
                                              All I've been doing in the last two weeks is working on petcocks. I convert them to manual to save a dime but I prefer vacuum ones (when working of course). If you have the bucks vacuum gives peace of mind but buy a new one now, you'll never know when that 30 year old one may crap out

                                                Comment

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