Bad Magneto? help!

Discussion in '2-Stroke Engines' started by rockvoice, Mar 21, 2009.

  1. rockvoice

    rockvoice Member

    Hey All, I helped a friend build his bike yesterday and it started ran good then we stoped took abreak and tried to start it again and it would not start.

    getting no spark (pulled plug turn motor and no spark on cooling fins). So got new plug, new plug wire, still no spark. now took CDI off my bike put it on his still nothing. is all thats left a bad magneto? Thanks in advance for any input. Rob...........

  2. srdavo

    srdavo Active Member

    maybe the sparkplug boot?

    double check your wiring & try it with the kill switch disconnected.
  3. srdavo

    srdavo Active Member can check the Similar Threads, at the bottom of this page.
  4. impression

    impression Member

  5. Revorunner

    Revorunner Member

    Sounds like a bad kill switch to me.Let us know what problem was when you find it.Curiosity Killed the cat.:grin5::grin5:
  6. rockvoice

    rockvoice Member

    fixed it thanks

    Hey , I finally used my head and stoped guessing. I pulled the magneto off my bike put on his fired right up! brand new motor bummer. so thanks for all your input. rob.........
  7. Mountainman

    Mountainman Active Member

    hi Rob
    yes that is a true bummer when it comes so fast on a brand new engine
    who ever your friend bought it from -- should send him a new magneto (((fast)))

    sure do like it better when it starts so as to ride that thing
  8. duivendyk

    duivendyk Guest

    Strictly speaking the coil that failed is not a magneto it is the power generator for the CDI unit.If you have a multimeter you can check the resistance to ground on the blue wire,should be about 330 Ohm and around 3 Ohms on the white wire.It is possible of course that there is a short between windings somewhere ,this would not necessarily show up in the resistance measurements.
  9. Revorunner

    Revorunner Member

    I'm confused here.

    In this post you said that you,and I quote{now took CDI off my bike put it on his still nothing.}

    So you took it off the first time and put it on your friends bike and it did not work.Correct?

    Then you took the CDI and put it back on your friends bike a second time and it worked.

  10. arceeguy

    arceeguy Active Member

    "Stator" would be the technically correct term, I suppose, but magneto seems to be an accepted and widely used description.

    I've run into a "no start" condition where the gap between the stator and rotor (magnet) was too large and it would not trigger the CDI. I loosened the mounting screws, shimmed the gap with a thin material (maybe .030") and the engine fired on the first pop of the clutch.
  11. rockvoice

    rockvoice Member


    Actually i said i tried the cdi from my bike to his and did not work then took the magneto off my bike put on his and it started right up. so it was a faulty mag.
  12. duivendyk

    duivendyk Guest

    Magneto's were pioneered by Bosch of Germany,early in the last century.They featured a horseshoe magnet and a rotating armature with a primary and a high voltage secondary winding.A magneto in general terms refers to a rotating device that generates a high voltage for firing spark plugs.The airgap is very important.The field strength and consequently the spark voltage is inversely proportional to the gap width.So if the system is marginal, an increase in the gap can be fatal.
  13. Junster

    Junster Member

    Clearance is critical for the stator to generate enough power for a good spark. A piece of notebook paper is about right to shim it with to get maximum spark. Same as normal lawnmower engine. Look for a stray wire sticking out of the faulty unit grounding it out.