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Running Lean VS. Intake Leak

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    Running Lean VS. Intake Leak

    Hi guys

    Finally got the bike running again - needed new starter motor brushes and now its like a whole new bike. also adjusted the valves, and cleaned/replaced Orings in the carbs. I vacuum synced yesterday and it seemed like it took a long time for the bike to be able to maintain an idle without the RPM gradually slowing down, eventually ending in sputtering and death. So I would bump the idle speed up a bit to compensate, which worked fine until the bike got more warmed up (about 5 minutes of running) and then the idle speed started climbing toward 2500-3000. Then I lowered the idle speed just bit and it seemed to even out at 1000-1200 RPM and held steadily. However, with a throttle blip it takes longer than it used to to return to idle. Engine braking seems to not be as strong either.

    So basically:
    --takes a while to get warmed up enough to maintain a steady idle without slowly tapering off and dying
    --slower than usual to return to idle
    --this is after complete dissassembly / rebuilding carbs and adjusting valves

    Some browsing on some posts here seem to suggest that this is either due to a overly lean mixture or intake boot leak. The mixture may very well be the cause, as I did remove the pilot screw for cleaning and I had the screws set at whatever was suggested in the guide on Bikecliff's site for BS carbs (1.5 or 2.5 turns out I think?). Haven't tried to adjust this yet, although I found a good post by koolaid kid on a technique for this.

    On the other hand, it could be intake boots, correct? The intake boots seemed supple and fairly soft. I would have changed them when the carbs were out anyway just to be sure, but the bolts just would not come loose (common problem on this bike I am finding). Several got stripped by my impact wrench before I stopped trying.

    Do these symptoms sound like they could be from the mixture, or do they definitely describe an intake leak? Is there a way to differentiate the two (without spraying flammable stuff around the intakes while its running, i heard this is bad practice)?

    and if I do enrichen the idle mixture, and these problems go away, do I still need to change the boots? I know that the recommendation is to just change them if there is any doubt. but its going to be a big PITA. if I can put it off for a little while, and enjoy the bike for a few weeks after having it not running for 5 months..... that would be nice.

    #2
    with the engine idling, spray some wd40 around the carb intake boots. if the idle speed changes then you have an air leak. are you sure you have freeplay on the throttle cables so the slides shut properly when the throttle is shut. also the cables and throttle tubes nice and clean and lubricated.
    1978 GS1085.

    Just remember, an opinion without 3.14 is just an onion!

    Comment


      #3
      whats a good lubricant for throttle cable?

      Comment


        #4
        Originally posted by ekabil View Post
        whats a good lubricant for throttle cable?
        wd40 or light oil, 3in1 that kind of oil, or any oil really is better than a dry cable
        1978 GS1085.

        Just remember, an opinion without 3.14 is just an onion!

        Comment


          #5
          Originally posted by ekabil View Post
          whats a good lubricant for throttle cable?
          Maybe a new cable is calling. By the way, have you thought about replacing the o-rings at carb boot/ head interface?
          Last edited by tom203; 04-10-2013, 06:13 PM. Reason: typo
          1981 gs650L

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

          Comment


            #6
            Originally posted by tom203 View Post
            Maybe a new cable is calling. By the way, have you thought about replacing the o-rings at carb boot/ head interface?
            from his first post......

            On the other hand, it could be intake boots, correct? The intake boots seemed supple and fairly soft. I would have changed them when the carbs were out anyway just to be sure, but the bolts just would not come loose (common problem on this bike I am finding). Several got stripped by my impact wrench before I stopped trying.
            1978 GS1085.

            Just remember, an opinion without 3.14 is just an onion!

            Comment


              #7
              Don't bother with WD-40, it is not a lubricant or a rust repellent, rather a Water Displacement - 40.
              For years I just dripped 3 in 1 oil down the cable; takes a while but it is cheap. I finally purchased one of those cable lube adapters and use the DuPont spray teflon from Lowes. Works great, very fast.
              How did you set the idle mixture on the carbs? To me it sounds like they need to be adjusted; check out the procedure link in my signature and see if that helps. Before I used it, I had the same symptoms. After you check for leaks, of course.

              Comment


                #8
                Spraying crap to try to detect an intake leak is a waste of time.

                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
                  Originally posted by Nessism View Post
                  Spraying crap to try to detect an intake leak is a waste of time.

                  but it works! always works for me anyway.........
                  1978 GS1085.

                  Just remember, an opinion without 3.14 is just an onion!

                  Comment

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