No spark test proceedure

Discussion in 'Electrical' started by KCvale, Aug 6, 2014.

  1. KCvale

    KCvale Motorized Bicycle Vendor

    This new build just a month old came in with a no spark condition.
    He was riding along just dandy and then it started to sputter out and die and wouldn't start again.


    I solder my re-wire of Magneto-CDI connection with better wire and use NGK Iriudium plugs so I can take some shortcuts but testing the components in the easiest most likely failure cause order works best.

    My no-spark troubleshooting procedure is simple these days and I threw in some solutions.

    First off if it was running fine and died that is one thing, if it never starts to begin with you have much more to check first like the plug and plug cap because they differ, basic wiring, etc.

    Assuming it ran, disconnect everything.

    Ohm the black magneto wire to a head bolt, it should read a dead short.
    If not, check the ground tab on the magneto.
    The new skyhawk CDI's have no white wire, ground is the lower connector but it has a wire from it to ground.

    Old style mags with a white wire have a tab out of the mag that solders directly to the mag base and they can come loose, just hold it down and re-solder.

    Ohm the magneto from the black and blue wire, 320-380 ohms is ideal, an open or dead short means a bad magneto if the blue wire and ground tab are connected.

    Ohm the CDI in the 10K-20K scale.
    Red+ meter probe to CDI black wire.
    Black- meter probe to the spark plug cap.
    You should get about 6.9K ohms.

    If not it could be a bad wire or cap.
    Unscrew the plug wire at the cdi, use pliers or even cut it off and dig the junk out if need be and do the same test above again to the cable screw on the CDI.
    If that works get a new wire and plug cap, if not you have a bad CDI.

    If all of that is good there is only one thing left, the magnet.

    That was indeed the problem with this repair on a new build with a 2014 front page engine kit.

    When you pull the 4 bolts out of the magneto mount it should slam itself against the magnet, I mean to the point where it is hard to even get your first bolt in.
    A weak magnet that lets you move the mag around pretty easily is not strong enough to create a spark which is what this repair had.

    Magnet replaced, problem solved and this really odd repair is done.
    Last edited: Aug 6, 2014
    Timbone likes this.

  2. OCCStingray

    OCCStingray Member

    The magnet, the one on the shaft?
  3. KCvale

    KCvale Motorized Bicycle Vendor

  4. stroland

    stroland New Member

    ive got a bad mag like to just rewind it. ive rewond motors for rc aiplanes so this will be easy . i just dont know if tis clock wise or counter clock wise,little help?
    Bike_Builder likes this.
  5. No Spark

    My bike looks identical to the one shown.
    I'm **** I order in this hong kong junk kit nearly zero instructions chain keep breaking deforming finally got it solved tried to compression start sput pop and thats it no spark I used volt meter out of the magneto befor the coil not even 1 volt can you show a picture of the ground tab where to find it that could be the reason but I took a jump wire grounded to engin bolt to the connector still no spark.
  6. Oh Ohms

    My magneto has 322 ohms my CDI has 8 ohms is this sick?
  7. danlandberg

    danlandberg Member

    What about blue wire on CDI? Any test?
  8. KenM

    KenM Member

    Hi KC, thanks for these tips!:p Very good to know. I wrote them down in my shop notebook , because I would never be able to find this thread again when the engine has no spark and I need to know this testing info!:)
    Thank you very much Sir!:cool:
    Keep looking up! Ken.