Discussion in '2-Stroke Engines' started by unraw, Sep 11, 2008.

  1. unraw

    unraw Member

    i have a power king 80cc motor om my 20" bike and it has no ignition. i have checked all the connections and took the whole ignition system apart and i cant find anything wrong. i did find a few pin holes in the wires so i replaced all the wires coming from the magneto. its not the coil. i checked with a different one and it still didn't work. so what is left to check?

  2. Mountainman

    Mountainman Active Member

    you may need to search here a little
    have seen posts that give readings (voltmeter) for magneto and such

    Happy Riding from - Mountainman
  3. unraw

    unraw Member

    ok I'll do that and see what i find. i kinda think that the magneto is burned out. I had the kill wire hooked up so it would ground out the ignition. after coming to these forums i found out its not good to do that.
  4. QuadManiac

    QuadManiac Member

    Measure across the blue and black leads of the magneto (disconnected from the CDI) with an ohm meter. If you measure relatively low resistance (mine measures around 320 Ohms) it is probably fine. If It's blown you will likely measure open (infinite) or very high resistance.

    With supplied kill switch shorting the bottom half of the magneto windings (the white wire), I suspect that eventually this ends up blowing the common ground leg between the two windings and so the spark generation voltage is also lost.
    Last edited: Sep 14, 2008
  5. unraw

    unraw Member

    I had the kill switch on the blue wire. does this make any difference from the white one? when i checked it im pretty sure it was open.
  6. QuadManiac

    QuadManiac Member

    On the blue will cause the same issue... shorting the blue to ground (just as shorting the white to ground) may well cause enough current to flow (briefly) for the winding to overheat, melt at the hottest point and open up.

    If it measures open, it's dead... It would be an interesting exercise, however, to find out where the break in the wire occured -unwind, locate, clean, solder, insulate and re-wind it; returning it to life. I did this once, about 30 years ago with a bad magneto on a Yamaha. Not hard, just a LOT of turns of wire to unwind and rewind. And in the rewing process, if you're close to the original number of turns, it's good enough. If you're off by say 50 turns out of a thousand, it will only make a 5% difference in the voltage output - not noticeable IMO.

    If one still wants to use the provided kill switch, I might suggest adding a resistor to one of the switch wires... I'll have to think a bit about the value. This would limit the shorting current to a value that won't kill the magneto. Since we know that the 6V leg is rated to about 1/2 Amp and I will assume that they use the same wire for both legs, I will assume that 1/2 Amp is safe for the HV winding also. Also assuming around 100V in the HV winding we can then solve for the resistor value that won't damage the winding. Using Ohms law - E = IR ---> R = E/I ---> R = 100 / (1/2) = 200 Ohm minimum value.

    So we'll have to see if the kill switch will still kill the engine with a 200 Ohm or so resistor in series between the switch and the blue wire, with the other switch wire connected to ground. I'll try this soon and report back. One thing for sure, this should limit the kill switch's shorting current to a safe value. Hopefully, it will drop the magneto's voltage enough to stop spark generation.

    The advantage of killing the engine this way is two-fold. It alllows you to continue using the provided kill switch (in my case, built into the throttle) AND it will significantly reduce EMI (electro-magnetic inteference) from the wire up at the bars which can cause havoc with a digital speedo.

    Guess waiting for football has me bored enough that i decided to write a small novel here. Hope I didn't bore anybody to death.

    Good Luck!
    Last edited: Sep 14, 2008
  7. wayde

    wayde Guest

    this the best way i found and it doesn't hurt the magneto

    Attached Files:

  8. wayde

    wayde Guest

    unraw- did you check your plug, plug wire/boot
  9. unraw

    unraw Member

    yup thats the first thing i checked. i guess ill order another magneto because im too lazy to un wind all that lol. thanks for all your suggestions!
  10. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Did you test it?
    Don't go ordering parts without testing first

  11. unraw

    unraw Member

    ya i tested it. it is wide open