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Strange idle behavoir on a '79 GS550

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    #1

    Strange idle behavoir on a '79 GS550

    I was starting up my '79 GS550 after it was sitting for a while, and found that as soon as I turned off the choke, the enginge would die, even when hot. I discovered that the idle RPMs were too low, so I adjusted them with the throttle stop screw until they were back up around 1100 RPM (using the Tach). It seemed to run fine, but half a mile down the road, sitting at a red light, with my hand off the throttle and the bike in neutral, the RPMs suddenly went up into the 3000 range. I turned the scre back down to get them to 1100, and it seemed to be working fine from then on.

    Any siggestion as to the cause of this problem? Could the stop screw just be loose and moving from vibration? I know I need to clean the carbs, could that cause this behavoir?

    Thanks,
    Tags: None
    #2
    MAYBE----- there is a bit of gummed gas in your system. Run gas treatment through a few tanks .

    Comment

      #3
      Re: Strange idle behavoir on a '79 GS550

      The idle passages in your carbs are starting to get gummed up. Disassemble and soak the carb bodies.

      Earl

      Originally posted by jgalak

      Any siggestion as to the cause of this problem? Could the stop screw just be loose and moving from vibration? I know I need to clean the carbs, could that cause this behavoir?

      Thanks,
      Komorebi-The light filtering through the trees.

      I would rather sit on a pumpkin and have it all to myself than be crowded on a velvet cushion. H.D.T.

      Comment

        #4
        it sounds to me like you have a leakey intake boot, and it is opening up and closeing on its own accord.


        try this and tell me if this does anything. run the bike in neuatral and set what you have to to get it to idle. next after you get it idleing spray some WD40 around each rubber intake boot connecting the carbs to the motor. do each boot seperatly and make sure to get the WD40 all the way around. As you spray each boot listen to the idle of the motor, if the idle picks up then you have a leaky boot and it needs to be replaced.

        what is happening is to much air is getting into the motor and making it lean in that piston and the WD40 closes the hole for a breif moment, with the leaky boot, does your bike also backfire alo on decel?

        -Ryan
        78 GS1000 Yosh replica racer project
        82 Kat 1000 Project
        05 CRF450x
        10 990 ADV-R The big dirt bike

        P.S I don't check PM to often, email me if you need me.

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          #5
          It's never backfired. I'll try the WD-40 test tomorrow.

          Comment

            #6
            Classic situation, the bike idles OK cold but idles too high when warmed up. You lower the idle and it seems OK. The next time you start it up cold the idle needs to be set up again...
            Usually an intake leak. Make sure the manifold clamps are tight. Next, spray a fine mist of water (cleaner than other sprays) on each manifold and listen for an rpm drop. Spraying the manifolds does not ALWAYS expose the leak because it can be hard to get full coverage. If your clamps are tight, I bet you need new o-rings in the manifolds. They're cheap, get all 4. Apply some hi-temp bearing grease to them to help them last and torque the manifold bolts to 6 ft/lbs to avoid crushing the o-rings.
            And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
            Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

            Comment

              #7
              you know...i must be a rare case here, because my idle raises a little (500-700 rpm) when the bike warms up, BUT i have no detectable intake leaks. we did a propane test on it last week when it was running...and there were no problems.

              i'm gonna say its something with the carb jetting, but its not a big deal to me.

              i did have a sticky high idle situation, which resulted from my throttle linkage bar bolt coming loose...and the throttle would stick a little before it closed.

              i'm gonna agree with the other guys, that your bike had some clogged pilot jets. what happened was they cleaned up a little bit when you raised the idle, and eventually cleared up good enough to run the idle up high like you said happened.

              run the bike at idle, spray some carb cleaner through. if the problem persists, you'll have to drop the bowls and clean out things.

              ~Adam

              Comment

                #8
                Read through this:

                http://www.cycleorings.com/intake.html


                I don't sell these; you'll need them from the dealership.

                The suggestions for testing intake leaks are all pretty good. Personally, I prefer using ether, but the basic idea is the same.

                In a nutshell, though, consider this: If the intake boot O-rings haven't been changed in six years or so, they WILL cause you grief. They might or might not be the cause of this particular problem; however, when they get brittle, they mimic other problems -- problems that you'll spend time & money chasing. They make the engine temperamental. If you're going to pull the carbs, order these from the dealer first and change them while you're in there.

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