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  • #1

    Two petcock questions

    Question 1 -

    Anyone know where to get one of the brass gas line connections for a '79 Special? Easy or hard to install?







    Question 2 - Does anyone recognize this type of petcock? Built in "octy."

    Front


    Back


    Thanks in advance,

    Aches n Pains (Doug)
    1995 KZ100P
    Pods, jets, pipes, cam adjuster, oil cooler

    1977 Ironhead - custom build
    Hot engine, custom frame, KZ front and rear, high torque starter, alternator conversion, Progressive shocks, Thunderheart wiring, Dyna ignition, oil cooler, Dakota Digital instruments, etc.

    Sold all my XS's to Eastcoaster but still love to keep up with you guys. This is the best cycle forum on the web.
    Tags: None
  • #2
    The petcock is a vacuum unit found on XS1100 standards and many other Yamaha motorcycles. When functioning properly, it should reain off until vacuum is applied, then allowing fuel to flow. Moving the arm to the "PRI" position opens the valve with no vacuum applied.
    Marty (in Mississippi)
    XS1100SG
    XS650SK
    XS650SH
    XS650G
    XS6502F
    XS650E

    Comment

    • #3
      That is NOT the petcock from the standards Marty! Don't know what it is from.

      As to the missing nipple, if you do not use the octy then you could just plug that hole because it is only for prime and not needed with the octy gone.
      Nathan
      KD9ARL

      μολὼν λαβέ

      1978 XS1100E
      K&N Filter
      #45 pilot Jet, #137.5 Main Jet
      OEM Exhaust
      ATK Fork Brace
      LED Dash lights
      Ammeter, Oil Pressure, Oil Temp, and Volt Meters
      Green Monster Coils
      SS Brake Lines
      Vision 550 Auto Tensioner

      In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

      Theodore Roosevelt

      Comment

      • #4
        Originally posted by natemoen View Post
        That is NOT the petcock from the standards Marty! Don't know what it is from.
        The petcock in question 2 appears to be a vacuum operated petcock. I don't know when Yamaha started using them.

        I'm not sure if it's vacuum operated, but the one on this XS650D (1977) at least looks similar.
        Last edited by jetmechmarty; 02-22-2012, 08:55 PM.
        Marty (in Mississippi)
        XS1100SG
        XS650SK
        XS650SH
        XS650G
        XS6502F
        XS650E

        Comment

        • #5
          Originally posted by jetmechmarty View Post
          The petcock in question 2 appears to be a vacuum operated petcock. I don't know when Yamaha started using them.

          I'm not sure if it's vacuum operated, but the one on this XS650D (1977) at least looks similar.
          The 77 650 might use one that looks like that, but that's not quite what the ones the 1100 uses look like (similar but not quite the same). I can see a lot of hints to the similarity, but I can see a lot of difference as well. It's of the same general type, but only as being in the same family, not being the same part number or anything like that.
          Cy

          1980 XS1100G (Brutus) w/81H Engine
          Duplicolor Mirage Paint Job (Purple/Green)
          Vetter Windjammer IV
          Vetter hard bags & Trunk
          OEM Luggage Rack
          Jardine Spaghetti 4-2 exhaust system
          Spade Fuse Box
          Turn Signal Auto Cancel Mod
          750 FD Mod
          TC Spin on Oil Filter Adapter (temp removed)
          XJ1100 Front Footpegs
          XJ1100 Shocks

          I was always taught to respect my elders, but it keeps getting harder to find one.

          Comment

          • #6
            Originally posted by cywelchjr View Post
            The 77 650 might use one that looks like that, but that's not quite what the ones the 1100 uses look like (similar but not quite the same). I can see a lot of hints to the similarity, but I can see a lot of difference as well. It's of the same general type, but only as being in the same family, not being the same part number or anything like that.
            Agreed. The later ones all have plastic towers. Many of those look identical, but carry different part numbers. I haven't a clue what the difference might be between the fuel cock for a XS1100E and a XS650_2F. They look the same and the mount bolts will line up. That's just one example as there are a bunch of them.
            Marty (in Mississippi)
            XS1100SG
            XS650SK
            XS650SH
            XS650G
            XS6502F
            XS650E

            Comment

            • #7
              Aches N Pains,

              Steve did a write up on how to block off the PRIME port on the Special petcocks using a screw and a tap with some sealant. The port your missing the nipple to is the PRIME port, so as stated, if your not using the OCTY, you can simply block that hole of the petcock closed and be done.

              Having not owned a Standard just yet, I have no clue on the second petcock.
              Life is what happens while your planning everything else!

              When your work speaks for itself, don't interrupt.

              81 XS1100 Special - Humpty Dumpty
              80 XS1100 Special - Project Resurrection


              Previously owned
              93 GSX600F
              80 XS1100 Special - Ruby
              81 XS1100 Special
              81 CB750 C
              80 CB750 C
              78 XS750

              Comment

              • #8
                Octy

                About the octy:

                What is the point? So we can be lazy and not turn the valves 'off' without fear of over-filling bowls? Does the fuel delivery increase with vacuum draw as a makeshift fuel pump? I don't understand the point of the octy unless the bike was designed with a tendency to overfeed/underfeed itself on gravity.

                I just replumbed and considered eliminating it and running soley on gravity but didn't find any leaks/issues with the stock vacuum setup so I just left it. Any reason not to just eliminate the potential hassle?
                1990 Ninja ZX-10. It's the Silver Surfer. HI-YA!!

                2006 Yamaha XT-225. Yep, I take it on the interstate. It's Blue Butt.

                1982 Toyota 4x4. 22R Cammed, 38/38, 2" pipe, 20R head with OS valves, performance grind and other fun stuff. It's Blue RASPberry.

                1969 Ford F-250 Camper Special resto project. 390 RV cam, Demon carb, Sanderson headers, 2 and a quarter pipes with Magnaflow mufflers. It's Blue Jay.

                Comment

                • #9
                  Originally posted by jimbyjimb View Post
                  About the octy:

                  What is the point? So we can be lazy and not turn the valves 'off' without fear of over-filling bowls? Does the fuel delivery increase with vacuum draw as a makeshift fuel pump? I don't understand the point of the octy unless the bike was designed with a tendency to overfeed/underfeed itself on gravity.

                  I just replumbed and considered eliminating it and running soley on gravity but didn't find any leaks/issues with the stock vacuum setup so I just left it. Any reason not to just eliminate the potential hassle?
                  It's just a safety device. It is supposed to turn off the fuel whenever the engine stops. Anytime mine has failed, it has failed open. As for me, I don't see it as a hassle. I'm one of those people with a tendency to walk away with the fuel valve left on. I understand how it works and how it's plumbed, so I prefer to keep it. It can be removed without any adverse effect.
                  Marty (in Mississippi)
                  XS1100SG
                  XS650SK
                  XS650SH
                  XS650G
                  XS6502F
                  XS650E

                  Comment

                  • #10
                    Thanks for the info.

                    I have only experience specific to motorcycles from this bike when I have to do things to it, or elect to. My first reaction to the fuel system was "??" since any other carbureted non-pumped appartus I've used was simply gravity fed. I also thought the two valves were odd since any other bike I've ridden (not my bikes) only had one. Good to know that instead of having to rebuild the diaphragm if/when it breaks I can just go to a simple gravity feed. So far it works fine and I just put in new clear line and filters. As long as it works I don't plan on changing anything.
                    Last edited by jimbyjimb; 02-23-2012, 11:17 AM.
                    1990 Ninja ZX-10. It's the Silver Surfer. HI-YA!!

                    2006 Yamaha XT-225. Yep, I take it on the interstate. It's Blue Butt.

                    1982 Toyota 4x4. 22R Cammed, 38/38, 2" pipe, 20R head with OS valves, performance grind and other fun stuff. It's Blue RASPberry.

                    1969 Ford F-250 Camper Special resto project. 390 RV cam, Demon carb, Sanderson headers, 2 and a quarter pipes with Magnaflow mufflers. It's Blue Jay.

                    Comment

                    • #11
                      It's gravity feed whether that shutoff valve is there or not. It's just an open/close vacuum controlled switch.
                      Marty (in Mississippi)
                      XS1100SG
                      XS650SK
                      XS650SH
                      XS650G
                      XS6502F
                      XS650E

                      Comment

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