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  • #1

    Carb vacuum lines

    In reading the instructions for carb syncing, the manual says to remove the vacuum lines from #2 & 3 cylinder manifolds, and the rubber caps from manifolds #1 & 4.
    What are these vacuum lines supposed to attach to at the other end?? PO has the super-trick-screw-plugged-vacuum-line-remnants on all 4 manifolds, and I would like to make sure that whatever required vacuum from 2&3 gets it. I probably should have addressed this a lot sooner than now...
    Hi...my name is Mike, and I'm a lane-splitter.
    '80 XS1100SG (mine)
    '87 CMX450C Rebel (daughter's first bike)
    Tags: None
  • #2
    The vacuum lines on 2&3 are used to operate the two vacuum flow petcocks on my 80G, and the vacuum ports on 1 and 4 are capped off. When synching, the ports are used to indicate the vacuum draw on each carb. If you do not used the vacuum flow petcocks, then during normal motorcycle operation all ports are capped off. Do not get these confused with the back vacuum port that operates the vacuum advance mechanism located on the left lower engine.

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    • #3
      The vac lines on 2 and 3 run to the
      fuel petcocks to turn them on. Or to fuel octopus, for those unfortunates.
      John
      Now: '78 XS1100E 750 FD Mod (Big Dog)
      '81 CB900C ( 10 Speed)
      '78 CB750F ( The F)
      '76 CB400F ( The Elf)
      New '82 Honda MB5 Ring Ding
      Then: '76 CB550K
      '78 CB750F
      '84 VF1100S
      And still Looking!

      Comment

      • #4
        Re: Carb vacuum lines

        Originally posted by SanDiegoMike
        In reading the instructions for carb syncing, the manual says to remove the vacuum lines from #2 & 3 cylinder manifolds, and the rubber caps from manifolds #1 & 4.
        What are these vacuum lines supposed to attach to at the other end?? PO has the super-trick-screw-plugged-vacuum-line-remnants on all 4 manifolds, and I would like to make sure that whatever required vacuum from 2&3 gets it. I probably should have addressed this a lot sooner than now...
        Mike, do you have a clymers manual? I know on my 81 lh, one line goes to the vauum advance and the other goes to the octopuss. I just did the carb synch on mine...
        "If A equals success, then the formula is: A = X + Y + Z. X is work. Y is play. Z is keep your mouth shut." - Albert Einstein

        "Illegitimi non carborundum"-Joseph W. "Vinegar Joe" Stilwell



        1980 LG
        1981 LH

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        • #5
          Okay...got it now.

          Thanks for all the input...no octopus, so it all makes sense now. I need to sync the carbs, but I will have to make a home made tester...unless there is anyone in the North County part of San Diego (I'm in Oceanside) who has a REAL tester that would be willing to lend a hand??
          Hi...my name is Mike, and I'm a lane-splitter.
          '80 XS1100SG (mine)
          '87 CMX450C Rebel (daughter's first bike)

          Comment

          • #6
            Hi Potter,

            The line to the vac advance HAS to come from the spigot on the BODY of no2 carb...... not from the boot. If he advance unit is connected to the boot, it will bang back and forward, and mess up your timing.

            Any unused spigots on the boots must be capped off.

            AlanB
            If it ain't broke, modify it!

            Comment

            • #7
              Mike,
              You would need to ride up to Santa Cruz, but I DO have the mercury carb stiks. There may be help a little closer, LA area perhaps. I think I see a weekend ride with beer in you near future..
              Ray Matteis
              KE6NHG
              XS1100 E '78 (winter project)
              XS1100 SF Bob Jones worked on it!

              Comment

              • #8
                Closer

                Yorba Linda (Anaheim area) is lots closer than Santa Cruz. I have the motion pro mercury carb synchronizer too. Lots of others in the area have benefited from it. PM me if you're interested. I go to Vista often to visit the Wizard, but I don't take it with me...
                You can't stay young forever, but you can be immature for the rest of your life...

                '78E "Pathfinder" Show bike...
                Lovingly restored by Dave Delzell
                Drilled airbox
                Tkat fork brace
                Hardly mufflers
                late model carbs
                Newer style fuses
                Oil pressure guage
                Custom security system
                Stainless braid brake lines

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                • #9
                  Hi Mike,,,,I live pretty close,,,,Valley Center,,,and I am usually out your way surfing at the Harbor on weekends. I have a synch tool, so let me know if you need it. Its easy to use, just need a couple of flat screwdrivers for the carb screws. Again, let me know if needed, Mike in V.C. The Wiz also hooked me up with a nice restorable, hopefully, xs1100
                  mike
                  1982 xj1100 maxim
                  1981 venture bagger
                  1999 Kawi Nomad 1500 greenie
                  1959 wife

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                  • #10
                    Mike,

                    This doesn't have anything to do with your question, but I have seen a number of your posts and I have to ask. Is that you in your avatar or is it Silent Bob?

                    DB
                    I think I have a loose screw behind the handlebars.

                    '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

                    Comment

                    • #11
                      Hey DB...no that's not me...it's Silent Bob. I think his character is hilarious, and we have the same method of displaying our appreciation for (good) rock music
                      Hi...my name is Mike, and I'm a lane-splitter.
                      '80 XS1100SG (mine)
                      '87 CMX450C Rebel (daughter's first bike)

                      Comment

                      • #12
                        AlanB is so right about hooking up the vacuum advance to the intake boot. I have no idea how these vaccums lines go, I remeber when i first started my MS the advance was jumping all over the place.....which now explains probably a lot of my problems...

                        Peter.

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                        • #13
                          Does anyone know where that little vacuum hose fitting beside the really large one down by the tranny goes?? I've the big one can be vented down towards the bottom of the bike.

                          Tks
                          Peter.

                          Comment

                          • #14
                            That is the vent for the middle drive unit, and it is to be routed up behind, and over the airbox, and under the seat and secured by a small bracket that attaches to the bolt that secures the front of the airbox.
                            The big one is the crankcase vent, and it attaches to the top front of the airbox, right above the carb inlet boots.

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                            • #15
                              Oh okay tks......what about the vac feed for the fuel manifold and the other fitting between #3&4 carb is that to the air filter??

                              Cheers
                              Peter.

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