Spark issue has me stumped

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  • overboostin
    • Jan 2026
    #1

    Spark issue has me stumped

    hey, I have a 78 gs750. I get healthy spark on 1 and 4 but I'm having an issue with 2 and 3. The issue has remained after I've done the following tests:

    points upgraded to Dyna s
    12 v to both orange coil power wires
    .25v to both black and white coil wires when starting
    coil replaced with another

    ive switched spark leads, black and white wires to the Dyna and points prior and the spark travels so I've narrowed it down to somewhere in the black lead off the coil. This seems
    strange to me though because both black and white go to .25v when cranking so it appears to have power. The strange thing is when I press the starter button it won't spark but as soon as I release the button I get one quick spark. What do you all think?
    Tags: None
    • chuck hahn
      Forum LongTimer
      Past Site Supporter
      • May 2009
      • 25918
      • Norman, Oklahoma
      #2
      Shorted switch maybe???
      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

        • chuck hahn
          Forum LongTimer
          Past Site Supporter
          • May 2009
          • 25918
          • Norman, Oklahoma
          #3
          loose wires at the button??
          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

            • Guest
              #4
              Just so I'm clear, you're getting proper current from both pickups on the new Dyna S?

                Comment

                • RGM
                  #5
                  Check for cracks on your plug caps

                    Comment

                    • overboostin
                      #6
                      Tried a new starter switch, and I'm getting proper current from the pickups. I'm getting the same reading from both pickups, 12v on orange and up to .25 on black and white when cracking. Don't think it's the plug caps, I've tried multiple coils.

                        Comment

                        • posplayr
                          Forum LongTimer
                          GSResource Superstar
                          Past Site Supporter
                          • Dec 2007
                          • 23673
                          • Tucson Az
                          #7
                          Originally posted by overboostin
                          Tried a new starter switch, and I'm getting proper current from the pickups. I'm getting the same reading from both pickups, 12v on orange and up to .25 on black and white when cracking. Don't think it's the plug caps, I've tried multiple coils.

                          Voltage is like pressure and current is like flow rate so they are different. You could have those exact same voltage values and have little to no current in the coils. You would check the primaries using an ohmmeter or amp meter if you have that for a direct current measurement.

                            Comment

                            • Steve
                              GS Whisperer
                              • Jun 2005
                              • 35924
                              • southwest oHIo
                              #8
                              You should have ZERO on your black/white wires.

                              .
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                                Comment

                                • overboostin
                                  #9
                                  Tried throwing the points back on and it seems to have solved the problem so it looks like my dyna is dead unfortunately. I'll be ordering another one monday and keep the points as a spare. Thanks for the help guys.

                                    Comment

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