Measuring spark?

Discussion in 'Mechanic and Repair' started by bugspit, Apr 12, 2004.

  1. bugspit

    bugspit LawnSite Senior Member
    Messages: 767

    Is there a way to measure the coil output with an OHM meter?

    I'm down to my wits end, Homelite weed eater, rebuilt carb, replaced fuel tank last year, ran great for about 4 months.

    What it's doing now is it's hard to start, runs at idle only with choke on, give a little gas and dies.
    Been through the carb and fuel lines thinking it's starving but it appears OK. New fuel lines and filter included with tank.
    The spark looks weak to me.

    Being a Homelite, is it time to upgrade?
  2. BW4486

    BW4486 LawnSite Member
    Messages: 243

    Yes its time to graduate to a real string trimmer
  3. sdwally

    sdwally LawnSite Senior Member
    Messages: 386

    You can use a ohm meter to test resistance through the coil and compare with the reading from a new coil. However to test output of the coil you need a kV testor. There are costly testors that Snap-On sells that work well or you can buy one that fairly cheap that take the place of the spark plug. These you can see the spark jump from terminal to terminal and usually have a screw to adjust the gap. The wider the gap the higher the kV rating. Most small engines are under 5kV.
  4. J.Gordon

    J.Gordon LawnSite Senior Member
    Messages: 674

    It would be cheaper to buy a new coil than to buy a high-voltage tester. And when your coil gets warmer the resistance will change if not short to ground if it's bad thats when a lot of problems happen.
  5. barnard

    barnard LawnSite Senior Member
    Messages: 618

    Its not electrical it s fuel or throttle position would not affectit. Pitch it and get a good trimmer.
  6. bugspit

    bugspit LawnSite Senior Member
    Messages: 767

    Replaced it with a Kawa KTR27A, gonna save it in case a find another at a yard sale and use it for parts. The coil was worth more than I gave for it. Might be a backup or yard ornament one day.
  7. ProMo

    ProMo LawnSite Bronze Member
    Messages: 1,468

    have you checked the exhaust port?
  8. bugspit

    bugspit LawnSite Senior Member
    Messages: 767

    Yeap, the screen was about clogged up, cleaned it and tried it, removed it and tried, no difference.

    Acts like it's starving for fuel but I've cleaned, blew out, replaced fuel, I've done this twice.
    The spark is weak, I'm wondering if when gas is given the spark is not enough to ignite?
  9. Joe B J

    Joe B J LawnSite Member
    from Alabama
    Messages: 37

    Check the exaust port, not just the screen. Remove the muffler and make sure the port opening is clear.
  10. bugspit

    bugspit LawnSite Senior Member
    Messages: 767

    Damn near polished and ported it. It breathes out just fine.

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