No spark - CDI and Magneto Ohm meter troubleshoot

Discussion in 'Electrical' started by velzie, Jan 20, 2014.

  1. velzie

    velzie Member


    I have a grubee skyhawk 66cc. I rode my bike in rain and went through some puddles. The bike would not run so I had to pedal home. I let the bike sit for a few days. When it got below freezing i took it out for a quick spin but it would not continuously run and would cut out. I removed the top-end and did some port cleanup then put it back with the piston arrow pointing to the exhaust. The bike now will not give a spark. I have run the tests below as scubaru89 describes in his post:

    Magneto Check:

    Black/White----2 Ohms----------3.2 Ohms----------200

    Blue/White-----300-400 ohms------302 ohms------ALL

    CDI Check:


    -Blue/+Black---130-150K ohms---40-180(flash)----200

    +Plug/-Blue-----135-155K ohms---1500(flash)-------2000k

    Plug/Black------2.5-2.7 K-----------7.0----------------20K

    For the CDI values the readings just appear for a second then leave. Is that normal? Also, I'm not quite sure if the resistance values are in the right ranges.

    From the Bikeberry youtube tutorial the magneto leads give the same 302 ohm BUT the CDI leads do not show ANY resistance. This makes me believe that I fried my CDI by running in the rain.

    Any insight or suggestions are appreciated,


  2. jaguar

    jaguar Well-Known Member

    the only valid way to test is to meter the AC voltage at the wires coming out from the stator coil. Get 30-50 volts there pushing the bike and you know the stator coil and its ground connections are good. If good there then that just leaves the CDI, spark plug cap, and spark plug.
    velzie likes this.
  3. velzie

    velzie Member

    Hello Jag, and thank you.

    So hook up the multimeter to the blue and black wires coming from the motor to the red and black wires of the multimeter, respectively. Then push the bike with the clutch engaged to see 30-40 volts. I'm going to check the cap now. Then I'll push the bike around my living room. Its -15C(5F) outside...

    I have 3 spark plugs, 2 Chinese ones (one fresh and one used) and a used E3.12. None of them spark so I don't think its plug related. Its probably also good for me to note that the kill switch is not engaged either, so It isnt a short there.

    I think I read that the resistance jumping to a value then falling to null is normal for the CDI readings? Also that it is very possible for rain to have shorted the CDI. On a side noter where I live there is a lot of salt used to melt ice on the roads. The highly salted water increases conductivity which would increase shorts and rusting.
  4. jaguar

    jaguar Well-Known Member

    yeah the AC has a very low negative voltage when it is connected to the CDI (because the negative part of the waqveform is pulled down by low value resistors). Best to ubhook it so you get a true AC reading.
  5. velzie

    velzie Member

    Hi Jag,

    I'm getting about 37 VAC. And thats the voltage reading a 200V on the multimeter. The V has the squiggly line above that indicates alternating.

    I'll have to get a new CDI, but it probably wont be for a few months... I'm a little strapped for cash and the weather here won't be good for MBing until March/April. I'm beginning to hate where I live

    edit: there is continuity through the plug cap as well as the lead, so the problem is not there either...
  6. velzie

    velzie Member

    Although I am a little embarrassed to mention this, I do it to complete the story in the thread I started.

    My problem was that there was no connection between plug and boot - I am getting spark now. I seem to remember there should be a small brass piece connecting the boot terminal to the top of the spark plug. I no longer see that piece.

    The stock Chinese plug has a cap that screws off, so I screwed it off a little to make connection the the boot. This is what showed spark when grounding the plug to the jug and spinning the rear tire with the clutch engaged.

    THIS post by Al.Fisherman led me to solve the problem. I will try again to start the bike tonight even though its -24 C(-11 F) outside.

    Last edited: Jan 23, 2014