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79 GS 750 only running on two cylinders

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    79 GS 750 only running on two cylinders

    So i havent ridden the bike much lately. The battery was dead so i tried to jump it with my vehicle and it blew most of the fuses. I replaced them and now only cylinders 2 and 4 are running. I pulled #1 spark plug and it smelled slightly of gas. It was when i felt my exhaust that i knew which pistons were and were not firing. Is this a dirty carb problem or could in be electrical?

    #2
    Check spark by removing the plug caps in question, sticking a spark plug into the cap, and grounding the metal spark plug threads against the engine while cranking it over. If you see spark, the problem is unlikely to be that.
    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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      #3
      Could be a combination of the two. Get 4 new plugs..or clean the ones you have well with a wire brush and regap them. Then see if it fires all 4. Could be bad pljugs in the 2 cylinders or could be the carbs got gummed up a bit while sitting. You can unscrew the caps on the offending wires and cut about 1/4 inch of and put the caps back on with good wire to cap connections. Try all the obvious before you tear down the carbs though. Put a good plug in the wires and hold it against the engine to see if the wires all have spark...that kinda trouble shooting..I dont think its a coil problem. You said 2 and 4 are running . The one coil runs 1 and 4 and the other runs 2 and 3, so that tells you that both coils are firing. Points are good...one runs 1 and 4 and the other runs 2 and 3..if any of the coils or points had failed you would have lost cylinders 1 and 4 in a pair or 2 and 3 in a pair. But since you have 2 and 4 firing this tells me that neither the points or coils had failed.
      Last edited by chuck hahn; 01-08-2012, 02:26 PM.
      MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
      1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

      NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


      I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

      Comment


        #4
        thats for the help. Didnt know that about the coils. I will test the plugs and be back.

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          #5
          go to BIKECLIFFS WEBSITE and get the free service manual download. Yup, the coils and points work in pairs for the cylinders. 1/4 are a pair and 2/3 are a pair.
          MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
          1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

          NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


          I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

          Comment


            #6
            Choose the 8 valve service manuall
            MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
            1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

            NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


            I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

            Comment


              #7
              Originally posted by chuck hahn View Post
              Put a good plug in the wires and hold it against the engine to see if the wires all have spark......

              Do this and we might know if it's firing without even looking at it.
              Zap!
              sigpic

              82 GS850
              78 GS1000
              04 HD Fatboy

              ...............................____
              .................________-|___\____
              ..;.;;.:;:;.,;.|__(O)___|____/_(O)|

              Comment


                #8
                You dont hold the plug..you hold the boot...he wont get zapped.
                MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                Comment

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