Random sparking from spark plug

Discussion in 'Electrical' started by kevingkruse, Feb 11, 2012.

  1. kevingkruse

    kevingkruse New Member

    I have tried searching around for this problem but couldn't find anything to help, sorry if I missed a thread that contains my problem somewhere. My bike was working fine until one day I was pressing my killswitch randomly to make it backfire (I think it sounds funny :p, but probly not good for it?), then it wouldn't fire anymore. I would try to start it back up but would only backfire once or twice without starting. I thought maybe I blew my head gasket cas it was making that high squeaky noise so I replaced it, fixed the squeak but still backfires and doesn't start. So i thought it wasn't getting a spark, so I unscrewed the spark plug and turned the wheel while holsing the plug and it seems to only randomly shock me instead of a consistant flow of sparks. I replaced the plug and still same thing. I looked at the plug after each try and its very slightly moist but not drenched. I wouldn't think the CDI or magneto is broken or else it wouldn't spark at all. I also unplugged my killswitch to see if it got stuck but still same thing. All other gaskets seem good, I'm stumped on this one. Any thoughts?

  2. toojung2die

    toojung2die Member

    My spark was weak and intermittent when the engine was brand new. I bought a new CDI and magneto. The CDI was bad. I replaced it and that was it. Runs great. Now I have a spare magneto.
  3. motorpsycho

    motorpsycho Active Member

    well...duhhhh. the spark plug is supposed to only spark "randomly"....like this : spark, no spark, spark, no spark, spark....etc.
    There is a magnet on the magneto and the spark plug will only spark when that magnet is in a certain spot as the crankshaft rotates (this is called spark timing).
    are you sure it's getting fuel?
  4. Al.Fisherman

    Al.Fisherman Active Member

    LOL good one...You may of sheared the woodruff key (in the magnet) when you backfired it. When the piston is a TDC (top dead center, all the way to the top of the cylinder) this is the proper magnet alignment. Notice where the cutaway for the key is located.
    Last edited: Feb 12, 2012
  5. HeadSmess

    HeadSmess Well-Known Member

    theres also the boot of the plug itself. i find after a few hundred km or so that the little brass fitting inside shreds, leaves nice brass powder down the insulator, and the spark decides brass is far more appealing than attempting to jump the plugs gap!

    usually signified by a strange popping "crack crack" sorta sound when starting.

    when it gets wet (rain) i have to dry boot, plug and wire before i can start. once its warm, tis ok.

    depending on how your killswitch is wired, you probably burnt out the magneto :)

    cut the white wire off.
  6. kevingkruse

    kevingkruse New Member

    Well its not sparking every other rotation, more like every 10-20 rotations. And I'm sure the fuel is not an issue.

    I removed the magnet and looked at the woodruff key, I'm not sure how to tell how if its sheared or not, it looks ok to me but I don't know. I also checked the alignment for TDC and its looks right.

    I replaced the boot with an NGK and same problem. I had my killswitch wired green to black and yellow/red to blue. Would I just cut the white all the way to the coil solder?
  7. HeadSmess

    HeadSmess Well-Known Member

    a sheared key is obvious. if it pokes out above the crank by 2 or 3 mm then its fine.

    have fun replacing the magnet (superglue the key in place or use a screwdriver and some determination)

    yep. take the white off at the source! saves later frustrations.

    so. it sounds like your magneto has fried.

    multimeter, ohms...i think its around 300 or so between blue and black. anything majorly different = fried.

    check the lil blob of solder up on the top front corner of the magneto coil. often the internal wire fuses right there and can be resoldered...
  8. toojung2die

    toojung2die Member

    Sounds like the problem I had. I saw a few sparks, then nothing, then a few more. The engine wouldn't run but I got a backfire now and then. Bad CDI.

    Sheared means it's broken and cut in two. If it's one piece it's good.

    Cut the white wire off at the coil or tape it and tuck it away. Don't use the white wire. Eliminate it so it doesn't cause a problem.

    Can you afford some spare parts? A magneto coil, CDI and new spark plug are good to have in the tool bag when you ride any distance. My vote says if you replace the CDI you'll be happy. Get back and let us know.
  9. SdCruizer

    SdCruizer Member

    I use my white wire to ground the kill switch to the frame
    the 2 other wires go to my coil/cdi
  10. Al.Fisherman

    Al.Fisherman Active Member

    Last edited: Feb 13, 2012
  11. SdCruizer

    SdCruizer Member

  12. Al.Fisherman

    Al.Fisherman Active Member

  13. wan37

    wan37 Member

    Really you should believe al on this one sdCruizer.I had a 6 volt headlight just what the white wire is design for and it draws to much and engine would not run!!! You should cap it off,and not use it.
  14. james65

    james65 Member

    I had a problem similar to yours. Disconnect the kill sw and give it a try.
    Some times it can ark thru the kill sw itself. Sometimes a kill sw cable can get pinched with a ty-rap or get chafed. Either of those can cause your exact problem.

    If thats not it it might be something else(LOL).

    Bufu racing#1 likes this.
  15. motorpsycho

    motorpsycho Active Member

    using the white wire for anything will draw power away from the cdi, and affect spark.
  16. SdCruizer

    SdCruizer Member

    if you understand how a switch works the white wire is not being used at all until I press in the switch to kill the engine
  17. motorpsycho

    motorpsycho Active Member

    cut the white wire off...do not use it.
    All the white wire does is create an electrical problem if ANYTHING is hooked to it, that will have you chasing ghosts (just as you are now).
  18. SdCruizer

    SdCruizer Member

    sorry im not chasing any ghosts at all
    everything has been running beautifully since I built it

    again, if you know how a switch works nothing negative can happen unless the switch fails and grounds out to the frame or there is a short in the sheath of the wire and it grounds out.
    If I ever run into intermittent stalling issues I will look at the wire and the switch
  19. motorpsycho

    motorpsycho Active Member

    ok, here's a little senario for you then.
    When i built my first m.b. i hooked a headlight up to the white wire.
    the engine ran good and the headlight worked for about a month.
    and then all of the sudden my engine wouldn't run anymore and I had spark / electrical issues.
    I chased this problem for a few days until i decided to cut the white wire off the headlight to take it out of the equation.
    guess what, the engine started right up and has ran fine ever since.
    I tried to hook the headlight back up to the white wire with the engine running, and as soon as i would touch the headlight wire to the white wire, the engine would die.
    I always cut the white wire off, and cap the end of it on every bike i build with a china 2 stroke now.
    you don't need to hook the white wire to the kill switch either.
  20. SdCruizer

    SdCruizer Member

    could the light be burnt out in the socket causing a ground?
    Or just bad wiring in the light
    Just like you say if you touch it to the light and the engine dies its the same as me touching the white to the frame and my engine dies, its grounding out and shutting off.
    Check the light I bet its shorting out somewhere

    Ive been doing electrical work for 17 years now, I have no issues with wiring, running wire, connecting wire low voltage and high voltage

    Plus I have no instructions that came with my engine, they seller I got them from has instructions on his website
    Are they correct I have no idea but he builds these bikes and sells them, is really knowledgeable with them. So far everything has worked.