No spark. CDI?

Discussion in 'Motorized Bicycle Trouble Shooting' started by seefish33, Aug 5, 2014.

  1. seefish33

    seefish33 New Member

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    While on a cruise on my motorized bike the other day, it just bogged out and stopped running. since then it has not started. I can peddle it, release the clutch and the engine with turn over but will immediately die (i assume because there is no spark).
    I have since tested the spark by holding the spark plug up against the engine and turning the wheel, no spark.
    I have tested the currents in the wires from the magneto to the CDI and they are fine, but from the CDI to the spark plug there is nothing.
    Do I need a new CDI?
     
  2. crassius

    crassius Well-Known Member

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    first, hold the plug in your hand & hand against head bolt while you turn the engine - if you feel no spark, check the coil with a multimeter
     
  3. fischer550

    fischer550 Member

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    It could be a few things. First, try a new plug. Check the plug for spark by putting the plug cap on the plug and setting the plug on your engine head so you can see the end of the spark plug. Then, while looking at the plug, turn over the motor. If you see no spark, you have no spark and that could be a plug, cdi, or magneto problem.
     
  4. Davezilla

    Davezilla New Member

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    Check your magneto coil my measuring the resistance between the blue and black wires, if it ohms out at less than about 360 ohms or gives no reading (dead open) it's bad. These are notorious for going out, especially if water finds it's way in there from riding in the rain or condensation etc... also, keep that area very well sealed by using rtv where the wires come out and a Thin coat of rtv on the gasket. Typical ohm readings are about 360 to about 600 ohms, but they will still spark if slightly over or under this range.
     
  5. KCvale

    KCvale Well-Known Member

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    I literally just walked in from troubleshooting the same problem so I'll share the steps.

    Disconnect everything.

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

    If the black ground wire does not attach to the engine the spark plug has no ground to spark to.

    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 wires 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 gasbike.net 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 my repair is done.
     
    #5 KCvale, Aug 6, 2014
    Last edited: Aug 6, 2014

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