Inside Ring/Spring/Plunger Problem on Pet Cock?

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  • pmong
    • Mar 2026
    #1

    Inside Ring/Spring/Plunger Problem on Pet Cock?

    Hi,

    I posted earlier about a problem with my pet cock on a GS450GA. It would only run for about 3-4 miles when on fuel then die, even with a full tank. I am able to run it on reserve without a problem, other than it is very hard to turn the lever to that position. (Yes, doubled check with the manual and service manual, and the position is RES.) So got a rebuild kit.

    When disassembling the pet cock and looking inside from the front, I am puzzled by the shape of a part that looks like a ring/spring/plunger component. The item is thin, between about 1/8 wide, and sits in a groove. From what I gather from the service manual, that is used to mechanically push open the diaphragm when using PRIM. However, it does not seem to be the right of the shape, and and the tip is not in the correct location to push down the diaphragm.

    I am including a photo. The spring is at the bottom. For reference, the top hole on the cylinder wall is the FUEL intake hole.

    Does the spring look right?

    Thank you in advance.



    http://i194.photobucket.com/albums/z45/pmong9/InsidePetCockResized.jpg
    Tags: None
    • Gonzo
      #2
      I'm no expert and this is the first glimpse I've had inside a petcock, but that looks like a ring or a clip of sorts that got crushed out of shape to me.

        Comment

        • pmong
          #3
          Originally posted by Gonzo
          I'm no expert and this is the first glimpse I've had inside a petcock, but that looks like a ring or a clip of sorts that got crushed out of shape to me.
          Gonzo. Thanks. I think you are right. If the valve is not inserted correctly, then a tab inside the valve could fold that thin metal piece. Moreover, the pet cock is very hard to turn, which indicates that something is possibly wrong.

          I hope someone can confirm this diagnostic and knows what can be done to correct this. Otherwise, I would have to buy a whole new pet cock.

            Comment

            • SqDancerLynn1
              #4
              Just get another petcock from Z1 With what you spent on the rebuild kit it is sad!!! for a few dollars more you would have had a new petcock.. Just ONE of the reason why it is better to buy new

                Comment

                • kirkn
                  #5
                  I just had this same finding in the petcock of my '85 GS700E this past weekend. The little metal deal was all twisted and bent up. The end result was that the petcock wouldn't flow in the 'PRIME' position. It wouldn't properly open the valve. You're description is correct - when the petcock is moved to PRIME, that strip pushes the plunger open whether there's engine vacuum or not. BTW, when in that position, the petcock draws from the RESERVE tube within the tank.

                  I've reassembled the petcock without the metal strip and swapped the vacuum-controlled plunger's spring from one side to the other. This effectively eliminates the vacuum feature while still allowing an ON and a RESERVE position. However, this also means there's no way to shut off the petcock, which means you're depending on the carbs' needle valves to keep the fuel off overnight, etc.

                  I don't trust the carbs' needles to do this, so I'll just splice a shut-off valve in the line and be done with it. I really hate the vacuum-operated petcocks....

                  Kirk

                    Comment

                    • pmong
                      #6
                      Originally posted by SqDancerLynn1
                      Just get another petcock from Z1 With what you spent on the rebuild kit it is sad!!! for a few dollars more you would have had a new petcock.. Just ONE of the reason why it is better to buy new
                      Yeah, should have, could have. A lesson learned. However, given a limited budget, the rebuilt kit seem a good way to go at the time.

                        Comment

                        • pmong
                          #7
                          Originally posted by kirkn
                          I just had this same finding in the petcock of my '85 GS700E this past weekend. The little metal deal was all twisted and bent up. The end result was that the petcock wouldn't flow in the 'PRIME' position. It wouldn't properly open the valve. You're description is correct - when the petcock is moved to PRIME, that strip pushes the plunger open whether there's engine vacuum or not. BTW, when in that position, the petcock draws from the RESERVE tube within the tank.

                          I've reassembled the petcock without the metal strip and swapped the vacuum-controlled plunger's spring from one side to the other. This effectively eliminates the vacuum feature while still allowing an ON and a RESERVE position. However, this also means there's no way to shut off the petcock, which means you're depending on the carbs' needle valves to keep the fuel off overnight, etc.

                          I don't trust the carbs' needles to do this, so I'll just splice a shut-off valve in the line and be done with it. I really hate the vacuum-operated petcocks....

                          Kirk
                          Kirk,

                          Thanks for confirming this. I may take your approach. Right now, the pet cock is back on and uses the vacuum feature. As you say, the problem is no PRIM now. What happened the the old simple ON-OFF, and perhaps a RES? Guess the vacuum feature is useful to those who are forgetful.

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