weak spark on 750E common?

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  • drhermanstein
    #1

    weak spark on 750E common?

    I'm getting popping and banging on what appears to be a weak sparking 750E. Stator provides good voltage , new battery sits at 13.6 at rest. all plugs have a weak dull blue spark. wires and caps are all at 5.5k ohms.
    NOS wire harness on the way. I hope that will work.

    Fuel, carbs, and valves are all OK
    Tags: None
    • Billy Ricks
      #2
      Search for threads on adding a relay to get power to the coils directly from the battery instead of the stock harness.

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        • drhermanstein
          #3
          Originally posted by Billy Ricks
          Search for threads on adding a relay to get power to the coils directly from the battery instead of the stock harness.
          Great idea, I'll try that asap. I have a number of good waterproof relays that would work real slick.

            Comment

            • tas850g
              Forum Sage
              • Jun 2008
              • 1678
              • Jaffrey, NH
              #4
              what does a relay do?
              1979 GS850G
              2004 SV650N track bike
              2005 TT-R125 pit bike
              LRRS #246 / Northeast Cycles / Woodcraft / Armour Bodies / Hindle Exhaust / Central Mass Powersport

              http://s327.photobucket.com/albums/k443/tas850g/

                Comment

                • doctorgonzo
                  #5
                  Originally posted by tas850g
                  what does a relay do?
                  It's a "Must do" modification in my opinion. In the original wiring the hot wire for the coils passes through the kill switch and sometimes other switches on the bike. This causes (especially with 30 year old switches) resistance so the 12V that left your battery may be 11, 10, even 9 or lower volts by the time it hits the coil, translates to weak spark. You use a relay to wire a hot directly from the battery to the relay and from there to the coils so you get the full output of the battery for spark. The relay functions to cut that juice off and on when the kill switch is used, ignition is off, etc.... Search for "Coil Relay Mod" and you should find a nice pictorial on it. I am NOT an electrical guy and I did it in an hour.

                    Comment

                    • drhermanstein
                      #6
                      Originally posted by doctorgonzo
                      It's a "Must do" modification in my opinion. In the original wiring the hot wire for the coils passes through the kill switch and sometimes other switches on the bike. This causes (especially with 30 year old switches) resistance so the 12V that left your battery may be 11, 10, even 9 or lower volts by the time it hits the coil, translates to weak spark. You use a relay to wire a hot directly from the battery to the relay and from there to the coils so you get the full output of the battery for spark. The relay functions to cut that juice off and on when the kill switch is used, ignition is off, etc.... Search for "Coil Relay Mod" and you should find a nice pictorial on it. I am NOT an electrical guy and I did it in an hour.
                      Thanks for the suggestion. Did the mod. It started up even though plugs were likely fouled and wet!

                        Comment

                        • Guest
                          #7
                          Originally posted by tas850g
                          what does a relay do?
                          Coil Relay Mod
                          http://members.dslextreme.com/users/bikecliff/images/coil_relay_mod.html

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