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Petcock conversion from vacuum to manual

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  • Petcock conversion from vacuum to manual

    Sorry if I’ve missed posts elsewhere on this topic. I just purchased these 2 petcocks from eBay for my '79 Special https://www.ebay.ca/itm/274182125033. The PO had removed the “Octy” from the bike but I don’t believe it was ever done properly. Anyways, I do want to covert the system from vacuum to manual to avoid issues of leaking petcocks or accidentally leaving it on PRI setting and causing bigger problems. The petcocks I have have no ‘OFF” setting, only ON, RES and PRI. I read one post that said to simply plug or loop the vacuum outlet and it automatically turns it into another OFF…just nee to buy proper fuel lines and plug to do this. Is it really that simple? Does there not have to be vacuum to these types of petcocks to allow fuel to flow regardless of plugging or looping? Or do I need to return these petcocks and buy the manual (no vacuum) ones which appear to be more expensive. I just want to keep it simple. Any ideas or insight is much appreciated. Thanks.

  • #2
    The petcocks in the link you provided have the vacuum shutoff feature, you will need to run a vacuum line to each one from the carb manifold boots. Just remove the caps on #2 and #3 and run the lines from those. The petcocks will then automatically shut off fuel when the engine is turned off.
    Last edited by bikerphil; 08-04-2022, 10:41 AM.
    2H7 (78)
    2H7 (79)
    3H3

    Comment


    • #3
      Is your XS1100 a standard?

      https://yamahaxs650.com/product/petc...n-vacuum-type/ Petcock – Non Vacuum Type



      Marty (in Mississippi)
      XS1100SG
      XS650SK

      Comment


      • #4
        Thanks gents. My apologies for my XS ignorance, ....so I see that it's easy enough to run vacuum lines back to #2 and #3 and keep the vacuum petcocks I purchased, but what was the purpose for the original octopus diaphragm and cock piping, which I do not have? Is that what is meant by bypassing the Octy?
        Attached Files

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        • #5
          Originally posted by jetmechmarty View Post
          Is your XS1100 a standard?

          https://yamahaxs650.com/product/petc...n-vacuum-type/ Petcock – Non Vacuum Type


          It's a special Marty.

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          • #6
            Originally posted by Hawkinspickle View Post
            Thanks gents. My apologies for my XS ignorance, ....so I see that it's easy enough to run vacuum lines back to #2 and #3 and keep the vacuum petcocks I purchased, but what was the purpose for the original octopus diaphragm and cock piping, which I do not have? Is that what is meant by bypassing the Octy?
            The Specials have manual petcocks. The vacuum shutoff valve (octy) is a safety device to stop fuel flow if the engine stops running. The standard XS11 has no need for this as the vacuum petcocks do that function.
            Marty (in Mississippi)
            XS1100SG
            XS650SK

            Comment


            • #7
              The Specials also have a DIFFERENT bolt hole spacing! A Standard petcock will NOT fit a Special tank, as the holes are about 8mm off. All I did on my Special is run a 4mm tap into the front outlet of each petcock, and put a short button head bolt into it with some JB weld gas proof as a sealer. They have been working well for over a year.
              Ray Matteis
              KE6NHG
              XS1100 E '78 (winter project)
              XS1100 SF Bob Jones worked on it!

              Comment


              • #8
                Originally posted by DiverRay View Post
                The Specials also have a DIFFERENT bolt hole spacing! A Standard petcock will NOT fit a Special tank, as the holes are about 8mm off. All I did on my Special is run a 4mm tap into the front outlet of each petcock, and put a short button head bolt into it with some JB weld gas proof as a sealer. They have been working well for over a year.
                I believe the OP has a standard. Although it wasn't specified.

                EDIT: I missed a post. Per Ray's post, you can't use the fuel valve I posted. You can't use vacuum petcocks.
                Last edited by jetmechmarty; 08-04-2022, 11:58 AM.
                Marty (in Mississippi)
                XS1100SG
                XS650SK

                Comment


                • #9
                  What is the bolt spacing on the Special petcocks? Now, after a careful read of the OP, I see "Special." I'm sorry, folks.
                  Marty (in Mississippi)
                  XS1100SG
                  XS650SK

                  Comment


                  • #10
                    Originally posted by DiverRay View Post
                    The Specials also have a DIFFERENT bolt hole spacing! A Standard petcock will NOT fit a Special tank, as the holes are about 8mm off. All I did on my Special is run a 4mm tap into the front outlet of each petcock, and put a short button head bolt into it with some JB weld gas proof as a sealer. They have been working well for over a year.
                    Hi Ray, so I take it from your response that plugging the front outlet of each petcock by putting in a button head bolt was don on "vacuum" type petcocks ?. Sorry to belabour this, but I need to understand that plugging a vacuum type petcock in the way you say does not affect the fuel flow as I thought that these types of petcocks needed vacuum to work properly, or does it just become a "manual" petcock if you do this? Just want to be sure before I plug the vacuum outlet. Thanks,
                    Dan

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                    • #11
                      The Special does NOT have a vacuum petcock. It uses the "octy" as we call it, for the vacuum switch to keep the fuel off when the engine is not running. Because of this, the Special petcock has two fuel nipples on it, not one. The front nipple is for the "prime" only, and is piped so that in prime fuel will bypass the octy and flow to the carbs. By blocking the prime nipple, no fuel can flow in prime so that does not need a fuel line. The petcock also has main and reserve, so just use those, and switch to the off position when parked.
                      Ray Matteis
                      KE6NHG
                      XS1100 E '78 (winter project)
                      XS1100 SF Bob Jones worked on it!

                      Comment


                      • #12
                        Thanks Ray, now I get it! The Octy on the Special was essentially and “satellite” vacuum instead of having the vacuum diaphragm on the petcocks itself. What was confusing me was that I didn’t realize that the PO had replaced the petcocks with manual ones but with only one nipple. I thought that they were originals for the Special. Now I understand that I cannot plug my new vacuum petcocks because they needs the vacuum. At least now I have the choice of either keeping the new vacuum petcocks and running
                        vacuum lines from #2 and #3 carbs OR getting another set non vacuum petcocks.
                        Wow. That was painful. Thanks for the clarifications.
                        Dan.


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                        • #13
                          Another way to run the fuel, single manual petcock on the left side feeding all 4 carbs with an electric octy in the line...
                          2H7 (78)
                          2H7 (79)
                          3H3

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                          • #14
                            Thanks, but I’ll leave that to the rocket scientists.
                            thanks all. Got great info.
                            Dan.

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                            • #15
                              Originally posted by Hawkinspickle View Post
                              I’ll leave that to the rocket scientists.
                              Even a plumber can do it.
                              2H7 (78)
                              2H7 (79)
                              3H3

                              Comment

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