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High/ Runaway Idle

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  • #1

    High/ Runaway Idle

    I haven't posted in a while, sorry, but everything has been fine and I've just not been online much. I also did a few searched, but since this forum doesn't seem to allow "and" modifiers, and it seems every other thread includes the word "idle."

    Had the gas tank off my 81 standard (With a 79 motor) for re-treating and moding, and had pulled the carbs off with the intent of perhaps cleaning. That was last...September perhaps. Never did anything with the carbs before the tank came back, and am now trying to put the whole thing back together.

    The bike starts just fine, but the idle runs very high (Broken tach stops at 6k, and it's over that.), there is still throttle after that, and the throttle cable seems to be moving normally (ie, it isn't stuck open). Enricher is off, and I back the idle screw out so far I'm a bit worried about it. Hard to say if there was any change (So there probably wasn't).

    I'm going back out to make sure all the mixture screws are 1 & 1/4 turns (about all I could get from the searches), but am looking for other ideas.

    Thanks

    Pain
    I've been in more than one Hemisphere, and I wrote a book to help you do it too (or just prepare better for that week long road trip). Going Small, not just for the little guys.
    Tags: None
  • #2
    Look for a vacuum leak...
    Ken Talbot

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    • #3
      Originally posted by Ken Talbot View Post
      Look for a vacuum leak...
      How? And do you mean the hose from the carb to the left of the engine, or the lines from the petcocks?
      I've been in more than one Hemisphere, and I wrote a book to help you do it too (or just prepare better for that week long road trip). Going Small, not just for the little guys.

      Comment

      • #4
        I believe Ken is referring to the boots between the carbs and the head. Also seems I have read somewhere about a vacuum leak at the advance or perhaps the synch being off such that no 2 carb was open more than the rest causing the advance to kick in.

        Somewhere to start anyway. HTH
        Life is what happens while your planning everything else!

        When your work speaks for itself, don't interrupt.

        81 XS1100 Special - Humpty Dumpty
        80 XS1100 Special - Project Resurrection


        Previously owned
        93 GSX600F
        80 XS1100 Special - Ruby
        81 XS1100 Special
        81 CB750 C
        80 CB750 C
        78 XS750

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        • #5
          Check the vacuum caps on the carb boots. They can crack or become loose. The carb boots too can leak where they bolt to the head. Make sure the carbs are all the way in the boots and the clamps are tight. Did you bench sync the carbs? Finding vacuum leaks can be done with an unlit propane torch, or a can of carb cleaner or starting fluid. Just listen for a change in RPM when checking suspected area. Just some suggestions.
          2H7 (79) owned since '89
          3H3 owned since '06

          "If it ain't broke, modify it"

          ☮

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          • #6
            I'm just going to make a suggestion, it will take you about 30 seconds to change so just do it even if you don't think its the problem, and don't ask how I know....

            Loosen the clamps that holds the engine side of the center two carbs and rotate them so that the big nut/bolt part of the clamp is as far away from the throttle linkage as you can get it and still be able to tighten them. It may not seem like they are holding the throttle open but just move em to be sure!
            1979 xs1100 Special -
            Stock air box/K&N Filter, MAC 4-2 exhaust, Bad-Boy Air horn, TC fuse box, Windshield, Soft bags, Vetter Fairing, Blinkers->Run/Turn/Brake Lights, Headlight Modulator, hard wire GPS power

            Short Stack - 1981 xs1100 Standard - lowered for SWMBO.

            Originally posted by fredintoon
            Goes like a train, corners like a cow, shifts like a Russian tractor, drinks like a fish, you are gonna love it.
            My Bike:
            [link is broken]

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            • #7
              Okay, I think I actually knew that. Maybe my brain is a bit melted from the noise.

              No vacuum leaks, using a carb cleaner and spraying the boots. What's next? I hope there's something...
              I've been in more than one Hemisphere, and I wrote a book to help you do it too (or just prepare better for that week long road trip). Going Small, not just for the little guys.

              Comment

              • #8
                Okay, if there's no leaks from the manifold boots, or from the caps on the vacuum nipples on the manifolds, or from the hose leading to the vacuum advance, I would suspect something mechanically interfering with the linkage at the carb end of the throttle cable like psychoreefer suggests. You could try taking the cable end right out of the linkage and see what happens.

                Another thought, how much slack do you have in the throttle cable? You shold have to twist the throttle a small amount before the slack is taken up and the butterflies start to move. If there's no slack, it may be as simple as adjusting the cable slack adjusters.

                Oh, and another thing, if the carbs have been off, and no matter how much or how little was done to them, you'll want to re-sync - when you get that idle speed down.
                Ken Talbot

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                • #9
                  I'm done tinkering for tonight, but will look at the throttle cable tomorrow.

                  There is slack in the cable, but that doesn't mean that the boot isn't holding it open some.

                  As for re-syncing, one that at a time, K?
                  I've been in more than one Hemisphere, and I wrote a book to help you do it too (or just prepare better for that week long road trip). Going Small, not just for the little guys.

                  Comment

                  • #10
                    Pull the carbs and make sure the butterflies are going all the way down. I sucked a small piece of plastic into my #1 carb the plastic stuck to the butterfly holding it open a 1/8". I had checked the slack in the cable and didn't notice much difference.
                    1978 XS1100E
                    1977 KZ750 Twin
                    1973 Suzuki GT750 "Water buffalo" 2 stroke (project)

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                    • #11
                      sync

                      I had the same problem definatly sync
                      91 kwaka kz1000p
                      Stock


                      ( Insert clever quote here )

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                      • #12
                        Well, the throttle linkage was bent, and hung up on the carb boot. I bent it back and now it starts and runs fine.

                        thanks, I promise to sync my carbs.
                        I've been in more than one Hemisphere, and I wrote a book to help you do it too (or just prepare better for that week long road trip). Going Small, not just for the little guys.

                        Comment

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