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Any reason not to measure compression with the carbs off?

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    Any reason not to measure compression with the carbs off?

    I'm reshimming my valve clearances, and will have to wait for a shim or two, so after I clean off the old gasket material, I was going to start checking and setting up the carbs. Does anybody see a reason I can't check compression with the carbs off? It calls for the throttle being wide open to check compression, so it seems OK to me, but I HAVE been wrong before!
    1979 GS 1000

    #2
    How far are your shims off? If they are at least close, it won't affect compression much, but checking compression with the carbs off is no problem.

    .
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      #3
      I don't think the valves were ever adjusted

      They were ALL tight; The thinnest feeler gauge blade I have is .04 mm, and there wasn't clearance for that on any of them. Compression was 110, 105, 120, 110, which is marginally meeting spec. Several members here felt that the valve clearances could greatly affect the compression readings. So, as soon as I finish setting valve clearances, I'll revisit how much this engine needs.
      1979 GS 1000

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        #4
        Only issue I see is that the engine should be warm but go ahead anyway - the reading will be low but they should be consistent (hopefully).
        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

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          #5
          It should make no difference if carbs are on or off. All you care about is
          if the engine seal (ring and valve) is adequite with an open orifice from
          the intake side. i.e. open manifold. When the carbs are on the bike, you open the butterfly for air to be drawn in. When the carbs are off, it is
          an open motor with no restriction other than the intake valve.

          Good luck to you !!

          :-D\\/


          .

          Comment


            #6
            I thought compression should be checked cold.

            I'm systematically working my way up to a rejet with a 4-into-1 and the stock airbok, but just a K&N or Amsoil Ea without the filterbox. So, first the valves, then bench sync on the carbs, a repack of the muffler, then rejet, and finally syncing the carbs. With the compression check, I'll get some idea of the state of this motor.
            1979 GS 1000

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