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Only firing cylinders 2 and 3 - Timing off?

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    Only firing cylinders 2 and 3 - Timing off?

    Hi,

    I have a '81 GS550L and got the bike running this morning after installing a Dyna S ignition and rebuilding the carburetors.

    I noticed that the bike only runs on choke and dies with throttle or when I take the choke off and decided to check the plugs.

    Only plugs 2 and 3 have any kind of soot on them, while 1 and 4 have no soot.

    Is this a problem with the timing? 1 and 4 are not firing at the correct time?

    I am new to all of this so sorry if this is obvious.

    Thanks,
    Kyle

    #2
    first I’d pull those plugs, plug them back in to their caps and one at a time, touch the threads against the engine as you crank. Should see spark. if you do, problem is likely fuel/carbs. If you don’t see spark....

    1 and 4 are fired by the same coil, so I’d look at the voltage in from both wires to and at the front of that coil and the voltage out of both HT leads from the coil at the plug caps.

    did the bike run before? What changed? Did something happen to cause the timing to be off?
    Rich
    1982 GS 750TZ
    2015 Triumph Tiger 1200

    BikeCliff's / Charging System Sorted / Posting Pics
    Destroy-Rebuild 750T/ Destroy-Rebuild part deux

    Comment


      #3
      Was running 6 months ago but throttle cable broke and decided to call it for the winter, took some parts off the bike to re-paint. Emptied the carburetors immediately in the winter and rebuilt them recently with a kit as the jets were all stripped. Then added the Dyna-s recently as well. Today was my first time starting it since the winter.

      I've checked for spark as you said earlier and all 4 plugs were giving spark.

      I will check the voltage as you say soon.
      Last edited by Guest; 05-07-2020, 06:02 PM.

      Comment


        #4
        I just checked the timing as well. If I'm correct, the timing marks from left to right go TDC, Firing, Fully advanced? So if I rotate the engine clockwise, I would go fully advanced, firing, then TDC according to the fixed mark? So when I attach the test light and I rotate clockwise in that order with the advance magnet fully turned clockwise, I get the light to turn on at fully advanced. I have the same situation if I move the test light to 2-3 and rotate the engine 180 degrees from the fully advanced symbol on 1-4.

        Comment


          #5
          High tension leads or high tension cables or spark plug wires or spark plug cables are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal combustion engine.

          So you have spark. I don’t see a need to measure the voltage. I’m sure there’s a way to measure it, I’m not sure exactly how you would now that I think about it.

          you say not soot on 1 and 4 plugs, those cylinder could just be running lean? but are you certain those cylinders not firing? Are those exhaust pipes cold?

          If their cold this would lead me to believe your issue is more fuel related than spark.
          Rich
          1982 GS 750TZ
          2015 Triumph Tiger 1200

          BikeCliff's / Charging System Sorted / Posting Pics
          Destroy-Rebuild 750T/ Destroy-Rebuild part deux

          Comment


            #6
            Double check your dyna-s connections...since it was running 6 months, it’s likely related to the new ignition. Don’t hesitate to call dyna about your issue
            1981 gs650L

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

            Comment


              #7
              I have nearly 400mV at cylinders 1 and 4 and 0 at 2 and 3 out of the HT leads, with 10V going into both coils.

              Does that make any sense since cylinders 1 and 4 aren't firing and they have voltage out the HT leads?

              Edit: I think this would make sense depending on what position the engine is turned over to?
              Last edited by Guest; 05-07-2020, 06:40 PM.

              Comment


                #8
                Yes, they're cold to the touch when I can feel 2 & 3 hot. I just checked the float bowls and 1 and 4 both have fuel in them.

                Comment


                  #9
                  10v little low but shouldn't stop it running. If you have sparks on 1-4 and the timing is right (just follow the Dyna S instructions) then I imagine your pilot circuit is blocked or something else in those carbs you just rebuilt...

                  Did you get the KL kits? Those don't get much love round here...
                  1980 GS1000G - Sold
                  1978 GS1000E - Finished!
                  1980 GS550E - Fixed & given to a friend
                  1983 GS750ES Special - Sold
                  2009 KLR 650 - Sold - gone to TX!
                  1982 GS1100G - Rebuilt and finished. - Sold
                  2009 TE610 - Dual Sporting around dreaming of Dakar..... - FOR SALE!

                  www.parasiticsanalytics.com

                  TWINPOT BRAKE UPGRADE LINKY: http://www.thegsresources.com/_forum...e-on-78-Skunk/

                  Comment


                    #10
                    How would I check if my pilot circuit isn't blocked? If my cylinders 2 and 3 are firing, would I theoretically be able to unplug the spark plugs, turn over the engine a few times and all of my plugs should be wet with gasoline?

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