1979 Special with Unknown MNS Motor Questions

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  • 79xs1100s
    Truly XSive
    • Aug 2009
    • 115

    #16
    I have the Resistor bypassed for the Dynas, but I assume that would be the same to go to stock 81 coils. All I did was unplug the old unit and plug in the new one without changing anything.

    So now the run down is...

    79 Special harness
    Bypassed Resistor
    3 Ohm Dyna Coils
    "81" Vac and Mech timing advance
    79 Special Carbs
    4RO TCI

    Runs Great.
    XS11.Com resident Black Sheep

    Comment

    • Dbshea
      Truly XSive
      • Mar 2016
      • 133
      • Muskego, WI.

      #17
      Originally posted by 79xs1100s
      I have the Resistor bypassed for the Dynas, but I assume that would be the same to go to stock 81 coils. All I did was unplug the old unit and plug in the new one without changing anything.

      So now the run down is...

      79 Special harness
      Bypassed Resistor
      3 Ohm Dyna Coils
      "81" Vac and Mech timing advance
      79 Special Carbs
      4RO TCI

      Runs Great.
      Good deal. That'll be the same recipe for me. Thanks for the update.
      79 F

      Comment

      • 3Phase
        XS-XJ Super Guru
        • May 2008
        • 5529
        • Simi Valley, CA

        #18
        Y'all are totally overthinking the ignition system, the ballast resistor is used to limit the normal running current going through the stock 1.5 Ohm 1978 to 1980 ignition coils, it's not for the TCI.

        If you're using the '78 to '80 coils or some other ~1.5 Ohm coils it doesn't matter which TCI you have -- use the ballast resistor.

        If you're using the '81 coils or some other 3 Ohm coils it doesn't matter which TCI you have -- do not use the ballast resistor.

        -- Scott
        _____

        2004 ST1300A: No name... yet
        1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
        1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
        1979 XS1100SF: "Bush" W.I.P.
        1979 XS1100F: parts
        2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

        Comment

        • Dbshea
          Truly XSive
          • Mar 2016
          • 133
          • Muskego, WI.

          #19
          Originally posted by 3Phase
          Y'all are totally overthinking the ignition system, the ballast resistor is used to limit the normal running current going through the stock 1.5 Ohm 1978 to 1980 ignition coils, it's not for the TCI.

          If you're using the '78 to '80 coils or some other ~1.5 Ohm coils it doesn't matter which TCI you have -- use the ballast resistor.

          If you're using the '81 coils or some other 3 Ohm coils it doesn't matter which TCI you have -- do not use the ballast resistor.

          Correct. We're on the same page about the ballast resistor and it's lack of association with the ignition unit. Coils need to match the ballast resistor, advance needs to match cams (as closely as possible in some cases) and the tci needs to match the advance. My biggest concern with the swap hasn't been components, it's been wiring. With only the one red/white coming out of the 4RO tci (and not having an 81 diagram to eyeball) I was afraid that circuit would feed the ballast circuit and not directly to the coils. Seems to be unfounded, which is good.
          79 F

          Comment

          • 3Phase
            XS-XJ Super Guru
            • May 2008
            • 5529
            • Simi Valley, CA

            #20
            You got it, no problems.

            For just about any conventional ignition, not just the XS11, don't use low-resistance coils with no ballast unless it was designed that way, it burns the ignition points or cooks the transistors.
            -- Scott
            _____

            2004 ST1300A: No name... yet
            1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
            1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
            1979 XS1100SF: "Bush" W.I.P.
            1979 XS1100F: parts
            2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

            Comment

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