1981 GS550L High Idle and Hanging Idle

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  • kylekochan
    • Jan 2026
    #1

    1981 GS550L High Idle and Hanging Idle

    What I've done to the bike:

    - Cleaned the carburetors
    - New intake boots
    - New airbox boots
    - New O-ring for intake
    - Weather stripped airbox
    - New and oiled air filter

    I set my pilot air screws at 2.5 turns and can start the bike and set idle to 1150~ but when I twist the throttle it will hang. So I have tested turning the pilot air screws out .5 up until 4 turns out, and the bike will idle too high, still have hang, and the idle adjustment knob is completely turned out, closing the butterfly valve.

    I'm completely lost. Any advice would be great.
    Tags: None
    • Rich82GS750TZ
      Forum Guru
      Past Site Supporter
      Super Site Supporter
      • Jun 2018
      • 5568
      • Mifflinburg, PA / Land of Tar & Chip
      #2
      Do you have smooth throttle cable operation/lubrication? Does the throttle tube snap back when you let go? Does the routing of the choke cable foul the throttle linkage on the carbs, causing the throttle to hang or return slowly?
      Links
      ​

        Comment

        • kylekochan
          #3
          Yes, they've been lubricated and the throttle snaps back quickly when I let go. The cable returns correctly and has the correct slack as well...

            Comment

            • Rob S.
              Forum Guru
              Past Site Supporter
              • Dec 2013
              • 9387
              • New York City
              #4
              Double check for any air leaks. Then triple check.
              1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

              2016 XL883L sigpic Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

                Comment

                • Nessism
                  Forum LongTimer
                  GSResource Superstar
                  Past Site Supporter
                  Super Site Supporter
                  • Mar 2006
                  • 35787
                  • Torrance, CA
                  #5
                  Don't see 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

                    • kylekochan
                      #6
                      Wouldn't I need to adjust the pilot air screws until highest idle and then decrease to 1200~ rpm for vacuum synch? I'm getting 4000 rpm when I have highest idle with pilot air screws adjusted and the idle knob is completely unscrewed with the butterflies completely shut.

                        Comment

                        • Buffalo Bill
                          Forum Guru
                          Past Site Supporter
                          Super Site Supporter
                          • Jun 2008
                          • 6004
                          • New Buffalo, Michigan 49117
                          #7
                          Would worn emulsion tubes and needles cause hanging idle?
                          1982 GS1100G-
                          1990 GSX750/1127
                          1987 Honda CBR600F Hurricane
                          1985 Kawasaki GPz750

                            Comment

                            • Nessism
                              Forum LongTimer
                              GSResource Superstar
                              Past Site Supporter
                              Super Site Supporter
                              • Mar 2006
                              • 35787
                              • Torrance, CA
                              #8
                              Originally posted by kylekochan
                              Wouldn't I need to adjust the pilot air screws until highest idle and then decrease to 1200~ rpm for vacuum synch? I'm getting 4000 rpm when I have highest idle with pilot air screws adjusted and the idle knob is completely unscrewed with the butterflies completely shut.
                              Sounds like a vacuum leak somewhere, and a pretty good one at that. With such a large leak it may show up if you spray some WD-40 on the carb intakes and around the throttle shafts. Worth a try anyway.
                              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

                                • tom203
                                  Forum Guru
                                  Past Site Supporter
                                  • Aug 2010
                                  • 8925
                                  • Norway,Maine
                                  #9
                                  Are you absolutely sure that ?choke? is fully off...plungers completely retracted?
                                  1981 gs650L

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

                                    Comment

                                    • Wolfdogg40
                                      #10
                                      I am having what sounds like an identical issue on a 78 GS 1000. I have done all you have as well, very strange as it seems to run well otherwise.

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