Using a Multimeter to check spark

Discussion in 'Bike Mods, Performance, Maintenance & Repair' started by Badgadjit1, Aug 9, 2006.



  1. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    I was reading Eric Gorr's jetting info, and in the mechanical problem area he says to check if your getting a good spark with a multimeter. I do have a digital multimeter but what and where should i place the testers (wires) and what setting should i have the multimeter set at, theres a bunch of settings.


    this is what i have.
    http://en.wikipedia.org/wiki/Image:Multimeter.jpg

    Thanks!
  2. rmc_olderthandirt

    rmc_olderthandirt Subscriber

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    A multimeter won't test for good spark. I strongly recommend against having the multimeter even touch the spark plug wire!

    The easist way to check for spark is to remove the sparkplug, attach the spark plug wire, hold the threads of the plug up against the motor case and kick the bike over. You should clearly see a nice strong spark jump the plug.

    If you are not getting spark, the multimeter can be used to establish why not by measuring the coil resistance and comparing to the manufactureres specification.
  3. sparkysakitas

    sparkysakitas Subscriber

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    i think if you hook up multi meter to plug and kick it it would blow the internal fuse or fry the meter spark voltage is way higher than what meter is rated for
  4. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    okay...io just re-read the info:

    Weak sparkÑWhen the ignition coils deteriorate, the engine performance will become erratic. Normally, the engine will develop a high-rpm misfire problem. Check the condition of the coils with a multimeter.
  5. rmc_olderthandirt

    rmc_olderthandirt Subscriber

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    Your profile says you have a YZ250, CBRF4i, and Kaw 1125.

    Which bike are we talking about?

    If you have a known good coil then it is easy to make a comparison measurement on your suspect coil. Without a known good coil to compare against you will need to know what the expected resistance is. There is also a problem that an inexpensive multi-meter (if you paid less than $200 it is an inexpensive model) their accuracy on very low ohms is rather poor. Not a problem if you can measure a good one then the suspect one, but can be a problem trying to compare suspect to the written specifications.

    If you have the technical specifcations or a shop manual for your bike it should give you the expected ohms. Two of them, in fact: primary and secondary. The primary will typically be a very low number and measured across the two main contacts of the coil. The secondary will be a much higher number and is measured from the spark plug wire to one of the main contacts.
  6. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    talking about the yz250. not sure if its a weak spark or not. I haven't looked, but i don't rember it being extremely bright. i'll check it tommorw. and i don't have a known good one, they're expensive.
  7. sparkysakitas

    sparkysakitas Subscriber

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    no there not to expensive
    go to electric supply house
    get fluke model or greenlee or ideal
    good one there run you about 100$ or less
    just get digital one
  8. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    no i meant a good coil...but i did find in my manul about what rmc_olderthandirt said, should i test the wires while the bike is running or should i just kick the bike over while the wires are in palce?
  9. sparkysakitas

    sparkysakitas Subscriber

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    its not the price its the make
    greenlee, fluke,amprobe and ideal all make good inexpensive meters as well as some high priced stuff
    use them alot at work
  10. Papakeith

    Papakeith COTT Champ Emeritus Damn Yankees

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    neither. you disconnect the coil and test the resistance measured against a known value for a good coil
  11. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    so do i just stick the wire to each end of the coil? doesn't it need to have electricity going through it?
  12. Papakeith

    Papakeith COTT Champ Emeritus Damn Yankees

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    Nope, no electricity needed. Well, no external electricity needed. The meter will provide the electricity you need.

    For a given long length of wire made of a certain metal at a certain thickness there will be a known resistance. Take that same wire and wind it up with a coating that keeps the wires from actually touching. For the coil you take a resistance reading. You know what it should be. If the meter shows a much lower number you have probably melted some of the wire insulator inside the coil and the spark that is being produced is weaker than it should be. If you read infinite resistance, that means there is a break in the wire somewhere and there is no longer a continuous conductor for the electricity to pass through.
  13. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    the main contacts are the two tabs that stick out of the ends right? where its bolted on?
  14. rmc_olderthandirt

    rmc_olderthandirt Subscriber

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    Yeah, I have an inexpensive Fluke meter......

    If I want a good meter I will go and buy a good model of Fluke. They make real nice multi-meters.

    What they were thinking when they made this cheap one is beyond my comprehension. It is the biggest piece of !@#$ I have ever used. I suppose that's why they were giving them away........

    The bottom line is that it is really difficult to accurately measure something less than 10 ohms. The resistance of the meter leads starts to be a factor. Oddly enough, the old needle movement meters were actually better (when talking cheap meters) because they always had a "zero" knob that the electronic meters lack unless you get into the expensive models.
  15. Todesengel

    Todesengel Rookie DRN Member

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    LOL! I'm curious to know how many of you have actually felt the "kick" of the coilwire? My bike stuck wide open one time, and I panicked and pulled the spark plug wire off bare handed! And that magneto was spinnnin!! Man I don't even want to do that again! :yikes: :yikes:
  16. Badgadjit1

    Badgadjit1 Rookie DRN Member

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    hahaha....i've felt it checking the spark a long time ago..had my fingers bit close, learned my lesson to...haha
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