Does a motorcycle alternator run the spark plugs or does it run off the battery?

I'm having some prolem with my spark being weak (it's not the coils, plugs or wires), this happans after riding for 5 minutes of riding, as it runs fine when it starts up. Could the alternator not be putting enough voltage out to run the plugs and it doesn't use the battery (as the battery has plenty of juice when the bike dies).

4 Answers

  • pappy
    Lv 5
    1 decade ago
    Favorite Answer

    It's just like a cars electrical system. If the thing starts and runs and the battery is still charged then it's not the battery or altinator. What year bike? Yoour coils could be failing and not show it when cold. Or your ignition module coould be doing the same thing. What makes you say that the spark is weak? I would tryo to check things as soon as it cuts out.

  • 1 decade ago

    Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer.

    Some older bikes with points, needed the battery to charge the coil. Most bikes use the alternator.

    Does it have multiple coils? Perhaps the one you're checking is fine and the other is defective.

    If yes, check for spark at each coil. When coils go bad, they stop working when they warm up and magically start working again when they cool down.

    If the bike has CDI, the pick up coil may be bad (it's used like a set of points and tell the coils when to fire).

  • Anonymous
    1 decade ago

    The sparks run off the battery. the alternator is only there to keep the battery charged.

    If your engine is fading then I would suspect a fuel blockage.

  • 1 decade ago

    it has an alternator, so it's possible thats the problem.

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