Announcement

Collapse
No announcement yet.

Possible petcock fix?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Possible petcock fix?

    The petcock on my 1978 GS 1000 leaks fuel through the vacuum diaphragm. Fuel is sucked into the vacuum port on carb #3. I read somewhere that if the stop tab is removed so the petcock lever can be put pointing up it serves as an off. With the diaphragm o-ring removed fuel should flow as if vacuum opened the port. With the vacuum port plugged on the petcock to (stop the leak), the carb vacuum port plugged, the reserve position should work. When in the ON position fuel would flow, straight up position the fuel would be shut off. Is my thinking flawed?
    1978 GS 1000

    #2
    Is it possible? I say yes, because I did it , but I can't tell you how because it was more than 30 years ago. My stock diaphragm failed on my 83 1100e , the bike was less than 5 years old. The engine filled with gasoline. I did not want to buy a new petcock so I converted it to a
    manual petcock by plugging up some ports. If I remember correctly, off was the old on position and on is the old reserve position. I ran the bike like this for over 20 years and never had a petcock problem again. These days I just run a pingle duel outlet with reserve, which I am very happy with.
    1983 gs1100ed restro-mod. 1998 gsxr 1100 almost mint, 2019 kawasaki klx250, 2011 Beta 250 evo trials bike, 2017 Montesa 300rr trials bike, 2021 honda crf250rx woods weapon

    Comment


      #3
      Yep, except you shouldn't have to alter the petcock. Just cap the vacuum port on #3. Then, use Prime for ON and you don't have reserve
      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


        #4
        The way I tried to explain you would have an Off and still have a reserve. The most important would be the OFF position.
        1978 GS 1000

        Comment


          #5
          I want to say I agree with your thinking. Hard to say for sure without one in front of me. Pretty easy to test, you don't have a lot to lose to do some bench testing if it's knackered already.

          Note that filing the tab & turning it all the way around does work but you'll need to mark the position to off as sometimes it's not straight up and does leak. I'd make sure you have good float needles that can hold the fuel back on their own if I was going to do this.... (also in case you forget to turn it to off).
          1980 GS1000G - Sold
          1978 GS1000E - Finished!
          1980 GS550E - Fixed & given to a friend
          1983 GS750ES Special - Sold
          2009 KLR 650 - Sold - gone to TX!
          1982 GS1100G - Rebuilt and finished. - Sold
          2009 TE610 - Dual Sporting around dreaming of Dakar.....

          www.parasiticsanalytics.com

          TWINPOT BRAKE UPGRADE LINKY: http://www.thegsresources.com/_forum...e-on-78-Skunk/

          Comment


            #6
            Just wondering if there's a reason to modify this one instead of just fixing it? Rebuild kits appx. $12. Some here have had problems rebuilding them, but so far I've rebuilt at least a half dozen with no problems.
            1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

            Comment


              #7
              Originally posted by Big T View Post
              Yep, except you shouldn't have to alter the petcock. Just cap the vacuum port on #3. Then, use Prime for ON and you don't have reserve
              Easier, but you lose about 4 liters of tank capacity
              1983 gs1100ed restro-mod. 1998 gsxr 1100 almost mint, 2019 kawasaki klx250, 2011 Beta 250 evo trials bike, 2017 Montesa 300rr trials bike, 2021 honda crf250rx woods weapon

              Comment


                #8
                Originally posted by chris View Post
                Easier, but you lose about 4 liters of tank capacity
                How would you lose capacity?

                Yes, you lose the REServe function, but the PRIme draws off the bottom of the tank, so you can use it all (with no REServe).

                .
                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


                  #9
                  Originally posted by Kingjoel View Post
                  The petcock on my 1978 GS 1000 leaks fuel through the vacuum diaphragm. Fuel is sucked into the vacuum port on carb #3. I read somewhere that if the stop tab is removed so the petcock lever can be put pointing up it serves as an off. With the diaphragm o-ring removed fuel should flow as if vacuum opened the port. With the vacuum port plugged on the petcock to (stop the leak), the carb vacuum port plugged, the reserve position should work. When in the ON position fuel would flow, straight up position the fuel would be shut off. Is my thinking flawed?
                  Just buy a new one and go ride. I've learned my lesson over the years, once it starts acting up, stop the fretting, stop the over thinking, just buy a new one.
                  sigpicMrBill Been a GSR member on and off since April 2002
                  1980 GS 750E Bought new in Feb of 1980
                  2015 CAN AM RTS


                  Stuff I've done to my bike 1100E front end with new Sonic springs, 1100E swing arm conversion with new Progressive shocks installed, 530 sprockets/chain conversion, new SS brake lines, new brake pads. New SS fasteners through out. Rebuilt carbs, new EBC clutch springs and horn installed. New paint. Motor runs strong.

                  Comment


                    #10
                    In the straight up position it would act as an OFF position, regardless of the condition of the vacuum diaphragm/o-ring. You could use PRI as "on", which would draw from the "reserve" bottom of the tank and Straight Up as "off". Here are the different positions broken down:

                    Starting from the 12 o'clock position, I'm enumerating the ports on the petcock body:

                    1 - 12:00 - Top of petcock filter (regular gas inlet)
                    2 - 3:00 - Bottom of petcock filter (prime inlet)
                    3 - 6:00 - Through to the petcock outlet
                    4 - 9:00 - Blocked/Does nothing. Any other port "connected" to this is rendered "blocked".
                    5 - Center - flow actuated via vacuum - While open, gas can flow from the front to the back and out of the petcock outlet.

                    There are two slots in the petcock lever piece that each can connect two of #1-#5

                    On:
                    #1 <> #5 - Vacuum flow from top of petcock filter
                    #3 <> #4 - Does nothing

                    RES:

                    #2 <> #5 - Vacuum flow from bottom of petcock filter
                    #1 <> #4 - Does nothing

                    PRIME:

                    #4 <> #5 - Vacuum does nothing
                    #2 <> #3 - Un-interrupted flow between bottom of petcock filter and petcock outlet.

                    Straight Up:

                    #3 <> #5 - Vacuum actuated center connected to petcock outlet. Were the engine running, this would do nothing.

                    #1 <> #2 - Top of filter linked to bottom of filter - does nothing.
                    Last edited by sam000lee; 09-10-2020, 01:52 PM.
                    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
                    1977 GS550
                    1977 GS750 - Cross country trip thread

                    Comment


                      #11
                      It works perfect!! By removing the little stop tab so the lever can be straight up I have OFF. By removing the diaphragm o-ring I have ON (without needing vacuum) and still have a functioning RESERVE when in the RESERVE position. PRIME is no longer needed since vacuum is not connected. The filter screen is connected. I also added an inline filter to keep the fine rust dust from the carbs. I did leave the diaphragm spring out but you can do what you want.
                      1978 GS 1000

                      Comment


                        #12
                        Great info. Now if I decide I want to go back to the days when we had no auto. fuel shut-off & I needed to remember to turn the fuel off all the time I'll know how to do it. But for now I think I'll just keep the auto working. I don't need to waste any of the little memory I have left.
                        1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

                        Comment


                          #13
                          The reason I did this is my 42 year old diaphragm was leaking fuel, getting sucked into the vacuum port on cylinder #3. I replaced the diaphragm and in the process lost the rubber gasket with the four holes (on the lever side of petcock). I replaced that four hole gasket with an old one from a cb 750 to get by (I have a new one now, less than $5 on Ebay). I had a massive leak so unintentionally I destroyed the o-ring on the new diaphragm (my brain slips to neutral at times). Not knowing the size of the o-ring or wanting to replace it with one that would leak after time I went this route. I've read where aftermarket petcocks are junk and non fuel resistant o-rings are used in the cheap kits. OEM petcocks are about $300 for this bike. I did not want to lose the RESERVE function by just switching the lever to PRIME. I have four other bikes without vacuum petcocks. I can remember to shut the gas off. I thought this method was better than buying a Pingle manual petcock as many have done. You guys are GREAT, I appreciate this forum. I hope this can help someone.
                          Last edited by Kingjoel; 09-12-2020, 10:24 AM.
                          1978 GS 1000

                          Comment


                            #14
                            Great to hear you've got it worked out.
                            1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

                            Comment


                              #15
                              just a note but this "tab removal" for fuel OFF won't work for every petcock...for instance, not this one:
                              petcock part.jpg

                              ..turning the pictured nylon piece with a hole drilled right through 180 degrees does nothing. Fuel flows...

                              However, some petcocks on Suzukis don't use this particular part... their oh-so-similar part is hollow with a single hole drilled to the hollow centre and it does work to turn fuel OFF when tab removed and tap handle turned up.

                              Comment

                              Working...
                              X