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    List of causes for high idle?

    My stage-0 (making up for decades of neglect and wear/tear/aging) is not quite complete, buuut....

    I've got a high idle of about 1500. Not that high, but even with the idle knob almost removed, it's still too high.

    My petcock diaphragm is leaking (new one is on its way, I'm going for a rebuild, everything else looks good).

    The throttle tension adjustment at the carbs was set too high, and every time I put my throttle together, it pulled on the cable.

    My intake boots have been sealed pretty well with silicone (I know, I know, new ones are on my list), but I can't detect any significant intake leak either at the airbox on either side, or at the head, or where the airbox and carbs meet. There might be a little leak, but I don't think there's much of a leak.
    The intake boot O-rings are new.

    So - finally my question. What all can cause a high idle? Is there a throttle plate stop screw I could have missed?

    Obvious causes:
    Something pulling on the throttle cable (not happening)
    Intake leaks (don't think are happening, but it's hard to tell)
    Excess fuel intake (like through a leaking petcock diaphragm)
    Choke circuit sticking (nope)
    Incorrect jets (stock jets, intake, exhaust, and airbox as far as I can tell)

    I bench-synched the carbs, but I'm waiting to try to synch them with a home-made carb synch tool... once I figure out the idle.

    What am I overlooking?
    What else can cause a high idle?

    Cheers
    Last edited by Guest; 08-30-2013, 10:09 PM.

    #2
    You can lead a horse to water but can't make it drink...
    Ed

    To measure is to know.

    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

    Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

    KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

    Comment


      #3
      Neigh.

      In other words, I'd love to replace the carb boots, once I can afford to. I'm broke, not cheap.
      Last edited by Guest; 08-30-2013, 10:51 PM.

      Comment


        #4
        Air leaks

        Air leaks

        Air leaks

        Idle screw too high
        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


          #5
          Originally posted by Big T View Post
          Air leaks


          Air leaks

          Air leaks

          Idle screw too high
          ...also

          Pilot screws too lean

          Air leaks

          Air leaks

          NO VACUUM SYNC
          Ed

          To measure is to know.

          Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

          Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

          Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

          KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

          Comment


            #6
            i have had a worn mechanical advance cause high idle on a different brand its probably air leaks though
            sigpic Too old, too many bikes, too many cars, too many things

            Comment


              #7
              Originally posted by Nessism View Post
              ...also

              Pilot screws too lean

              Air leaks

              Air leaks

              NO VACUUM SYNC
              A-ha! Well, I'd like to vacuum sync them. I'm waiting on the petcock diaphragm to do that.

              See, I'm asking because I want to know if I should have a proper idle before I try to vaccum sync them.

              Not responding to idle screw, pilot screws all set to 2 turns out.

              I'll check the airbox side boots again tomorrow.

              How many ways can the airbox leak?

              Comment


                #8
                Set pilot screws to 2.5 - 3 turns.

                Plug vacuum line and vacuum sync...after you get the new intake boots.
                Ed

                To measure is to know.

                Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

                Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

                Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

                KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

                Comment


                  #9
                  Hmmmm. The air filter box on the parts fiche I'm looking at is rotated 90 degrees along the length of the bike. My airbox opening points out to the side, the fiche shows it pointing towards the sky.
                  That's weird, and my airbox seems to be attached how it should be.

                  Comment


                    #10
                    The parts fiche is wrong on most sites. Make sure you get filter element or bike will run poorly even with those new boots that you will need.
                    1981 gs650L

                    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

                    Comment


                      #11
                      And remember that Nessism is saying the intake boots - that's on the carb side not the airbox side. But it is still a good idea to replace both.
                      Cowboy Up or Quit. - Run Free Lou and Rest in Peace

                      1981 GS550T - My First
                      1981 GS550L - My Eldest Daughter's - Now Sold
                      2007 GSF1250SA Bandit - My touring bike

                      Sit tall in the saddle Hold your head up high
                      Keep your eyes fixed where the trail meets the sky and live like you ain't afraid to die
                      and don't be scared, just enjoy your ride - Chris Ledoux, "The Ride"

                      Comment


                        #12
                        Hmmm. Are the inside and outside plenum (airbox) boots supposed to be different lengths? Because mine are. And I can't get them to fully seat with pressure on them and/or the carbs any which way.

                        The airbox boots still seem fairly pliable, but yes... I do have an air leak on #4 carb holder/engine side boot. But there must be more than that, since even with the plug wire pulled off #4, it still idles up around 1100.

                        I absolutely hate pulling the carbs on this bike. It is a huge PITA, since the air(filter)box will not come out with the plenum in place, and the plenum won't come out with the carbs in place.

                        Comment


                          #13
                          Yeah, its a PITA but think positively- once done right (clean carbs, decent boots) you might not have to do it again.
                          1981 gs650L

                          "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

                          Comment


                            #14
                            Sprayed both starting fluid and soapy water in ridiculous quantities all over every seam in the intake system. No changes in idle speed or smoke or anything that would indicate a leak.

                            My homemade carb sync tool (which needs restrictors haha) showed that they were way off. I need to put the restrictors in them before I draw any conclusions from it though.

                            Comment


                              #15
                              Forgive my ignorance, but do you have VM or CV carbies on your 650GL?

                              If VM's, I think it's possible to have all the slides raised too high, due to their individual adjustment screws (under the carbie caps) being screwed in too far.

                              Go to the carbie adjustment article for VMs (I think it's in the GS Resources 'Garage' section, from memory), and follow the instructions for a bottom-up rebuild for your carbies. That way you'll eliminate any other causes of high idle, besides <drumroll!> leaking intake boots.

                              Comment

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