spark plug won't fire unless I'm touching it

Discussion in 'Electrical' started by stephen7689, Oct 4, 2016.

  1. stephen7689

    stephen7689 Member

    I'm pretty sure I got to ground it somehow but have no clue all I know is that it won't start and when I take spark plug out to test it I'll push the bike and get no spark but if I'm touching the threads or any metal part of the spark plug while pushing it I get a strong spark so what do I do to get it to spark without me having to touch and hold it

  2. crassius

    crassius Well-Known Member

    I usually hold it against the nut on the muffler - had one years ago on which the guy that painted it got paint on washers holding head on and had no ground to head - try checking that with a meter.
  3. jaguar

    jaguar Well-Known Member

    just put a cloth between your hand and the plug if you're afraid of getting shocked.
    the spark needs a return path which is ground which is the engine metal
  4. THowell1975

    THowell1975 New Member

    Do you mean that your spark plug isn't making good contact into the boot? I've gotten different spark plugs and boots from different vendors. Yours may have a little "nipple" on the end of the spark plug that needs to be unscrewed so it fits properly into the spark plug boot. Does that help?
  5. Tatter

    Tatter Guest

    I am having the same problem went thru and bought a magneto cdi and plugs still the same will not spark unless i hold the plug it it cause i have the cdi mounted on the frame where it is painted or what this is my daily driver to work so got to get it figured out plz helppp
  6. jaguar

    jaguar Well-Known Member

  7. Frankenstein

    Frankenstein Well-Known Member

    The CDI is normally in a plastic casing, the painted frame will not affect the CDI in any way or form.

    Sparks if you hold it? Well if you're doing that right then it's sparking inside the motor as well. Now that leaves you with not enough fuel/air, a weak magneto that will only make the plug spark outside the motor, or a faulty plug, but since you ran through getting new ones perhaps it's something you haven't thought of or maybe don't know about. Magnet on correctly on the crank? If it's installed upside down you'll still get a spark but it won't happen at the right time and you'll never get the bike running. Take the plug out and engage the clutch with the wheel and turn it till you can clearly see through the spark plug hole that the piston is in the highest position possible. This is normally called top dead centre.

    With the piston at top dead center (tdc) look at the magneto magnet under the mag cover. There's a slot for the key to keep the magnet in place, and the magnet is held down by a nut. You'll need to take the nut off to see the slot or judge it by the position of the magnet itself. The slot would be at "1 o'clock" on the magnet as it were being installed but the angle of the magnet would be a dead giveaway. Look at this pic. Just remember the piston needs to be at its highest point to make an accurate judgment. You can feel the highest point as well by holding a pen against the piston through the plug hole and feel for when the piston is at the very highest point. Look at pictures, first one is how the magnet is aligned when correctly installed in the motor with the piston TDC (sourced from Fabian) maxresdefault.jpg

    This next image is how the magnet will look if installed backwards, even with the nut on the magnet you'll be able to tell its wrong simply by the tilted angle, normally the magnet should be basically horizontal

    Even if this isn't your problem you'll have an idea of what to do in the future should you ever tear a motor down. Please keep up updated.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    The ground tab on the magneto is not making a ground.
    Easy to test with an OHM meter.
    You should show a short between the black wire and the head.
  9. Frankenstein

    Frankenstein Well-Known Member

    Why would it spark if it wasn't grounded?
  10. crassius

    crassius Well-Known Member

    sometimes the solder is loose, but weigh of wire holds it down until motor shakes it loose
  11. KCvale

    KCvale Motorized Bicycle Vendor