The 101 Association, Inc.
For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
"You can't wear out an Indian Scout"

Spark Plug Cable Upgrades

  • 31 Jul 2023 7:50 PM
    Message # 13234837
    John Lindberg (Administrator)

    When I was in Torrington building my motor, Tim mentioned the idea of upgrading the spark plug cables by exposing the inner copper wire, bending it upwards along the insulation, and soldering on an eyelet.  The idea, as I understand it, is to provide a direct connection between the "needle" in the Splitorf magneto the the copper conductor.

    I'm currently relying on the "needle" in the magneto to pierce the spark plug cable insulation and make a good connection with the copper conductor.  I'm experiencing some hard starting issues, and want to ensure this isn't the problem.

    Can anybody provide some details on how to ensure the spark plug cables are making good contact at both the magneto and spark plug ends?  Do you solder both connections?   Any other tips or suggestions?  Photos would be very helpful.



  • 02 Aug 2023 10:36 AM
    Reply # 13235555 on 13234837


    I've never seen the need to do any of that. I bead blast the pin in the cap, get it super clean. Gently push the wire against the pin to set a mark. Then lay the cable on the table and use a sharp awl to pierce the wire, through the center. The cable will now push on much easier. Unless the pin is broken off, it is plenty long enough to pass the center of the wire, touching the copper. Install the screw on plate tight. I took a wooden block, turned it to the ID of the face and filed two crossing slots in the face. This made a nice tool to grab the plate and screw it in or out.  Crimp and solder the terminals in. Measure resistance from brass contact to plug terminal, should be virtually 0, use an accurate meter.  

    If you'r having new starting issues, something changed.....  be sure the float level is as high as possible and the idle circuit is on the rich side. 

    When prepping my 24 chief for the 18 Cannonball, I was having starting issues when I went to a lower altitude. It was all carburation, lean in fact. Howard Wagner pointed out the correct starting procedure, which solved the problem:

    1. Full choke, throttle CLOSED, 2 or 3 stiff priming kicks. Should pop, or drip from the carb.

    2. Choke closed only 1 notch, slight throttle, spark retarded just a bit, ignition on (if applicable) and strong kick. 

    Usually works great, often popping on the prime kicks.  The most important thing he pointed out was that during priming, the throttle MUST BE CLOSED with FULL CHOKE.  This allows the idle circuit to draw up a rich charge. If the throttle is open, even a little, the idle circuit doesn't do much of anything.

    Also, close the plug gap to as low as .015, makes a mag model fire much easier!

  • 03 Aug 2023 3:08 AM
    Reply # 13235918 on 13234837
    Tim Raindle (Administrator)

    Got  a feeling it is a new cap, with slightly shorter pins ? Old ones are fine, but some of the modern replacement ones have a slightly shorter pin, which doesn't quite penetrate a slightly thicker plug lead fully. I have on occasion exposed a short length of the cable, soldered it up and formed an flat in the end, which I have then folded back under and pushed over the pin. 

    Also, yep, Murphy law of motorcycling, 99% magneto issues are in the carburetor, and 99% of carburation issues are in the mag. Check carb first. Has anything changed since it was starting easily ? 

  • 03 Aug 2023 3:12 AM
    Reply # 13235919 on 13234837
    Tim Raindle (Administrator)

    Also, when pushing a new lead onto pins, be careful not to use too much force, it is very tempting to squish it on with a blunt object, which can lead to splitting out the back of the bakelite/plastic compound. Better to pierce the lead a little with a fine bradawl first.

  • 03 Aug 2023 3:47 AM
    Reply # 13235925 on 13234837
    Tim Raindle (Administrator)

    As another aside, again, my memory fails me, but did you have a new rotor in there John ? Several of the new carbon brush free rotors have scored up new caps, on occasion, and caused a misfire with built up debris, which sort of negates the point. If not, have you checked the carbon tracking in the cap ? Soft brush often builds up a carbon ring which then allows the spark to track between contacts, causing a misfire. Sometimes takes a while for the brush to bulid up a glaze to it. Often needs cleaning off every 50-100 miles until brush has settled in. 

  • 04 Aug 2023 5:15 PM
    Reply # 13236798 on 13234837
    John Lindberg (Administrator)

    Thanks for the outstanding suggestions.  I'm always amazed at the level of expertise in this association.  I appreciate that you share.

  • 16 Aug 2023 4:42 PM
    Reply # 13241776 on 13234837
    John Lindberg (Administrator)

    Just wanted to thank Gene and Tim for their solid suggestions.  I pierced the insulation of the spark plug cables to make sure the pins on the mag were making contact with the copper core, and I cleaned carbon tracks out of the cap.  I also tried Gene's starting procedure, and it worked like a charm!  I was even able to start it hot after a 20-mile ride today, something that's been a challenge in the past.

    So nice that we have this forum and so many smart people willing to share.

  • 18 Aug 2023 6:42 AM
    Reply # 13242557 on 13234837

    Just something to put in the back of your head in case you or anyone else has the misfortunes of having the magneto pins break off due to someone using tough plastic led cable….. you can purchase a modelling tap and die set that goes down to 1 1/2 mm, use a male Deutsh pin electrical connector and put a thread onto it, drill and tap out magneto, screw it in and cut off on diagonal to length…. I had to do both my pins as someone previously had tried to solder a pin in place of a broken off one only to discover that it is extremely difficult to get enough heat to be effective 


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