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Xs400 no spark

Discussion in 'The Garage' started by Uzeba, Jul 12, 2022.

  1. Uzeba

    Uzeba XS400 New Member


    So I was at the lights about the take off and my xs400 died flat battery which is normal if use the headlights to much.

    Tryed kickstart a load of time occasionally the bike would run. When giving throttle would die. Ended getting towed home. Charge battery and the bike would crank no problems but no spark.

    Replaced Coil packs as that was the only old part left on the bike after the build.

    I now have CONSTANT power front the spark plug leads before the caps 12.45v when ignition is on. Which I'm pretty sure shouldn't be happening.

    What are your thoughts guys?
  2. Myron

    Myron XS400 Member

    A coil has a ground bolt to chassis and two wires. One wire is 12v all the time with the key on. The other wire goes to the ignition points. There is some cool physics going on inside the coil. As I understand it, the battery side of the coil creates a big magnetic field and the points side holds the field back away from the sparkplug and when the points open, the magnetic field slams the volts thru the spark plug wire.
  3. Kitchi

    Kitchi XS400 Member

    do you have points or a TCI ignition?
    If you have a TCI ignition it would be normal to have 12 volts on the primary side of each coil (it will ground though the TCI box)

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