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What is the effect of low primary coil resistance

Discussion in 'Hangout Lounge' started by tabaka45, Jan 23, 2018.

  1. tabaka45

    tabaka45 Well-Known Member

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    I can't seem to find an answer to this, so hopefully one of you electrical or ignition experts can give me the answer. The specs for a Yamaha Grizzly 80 call for 1.4 to 1.8 ohms resistance for the primary side of the coil. I got almost zero on the original so I ordered a new one. I only get .6 ohms on the new one. Thinking it might be my cheap multimeter, I tried another meter with the same results. Then I bought a Mastech multimeter and still get .6 ohms. (The secondary resistance is right in the specified range. The engine runs on the original coil, but I seem to be having some problems with idle and starting sometimes. Secondary resistance on the original coil is a little high.) So my question is: what effect will the lower primary resistance have? Will it mess up the CDI or amy other part of the ignition?
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    the coil is an inductor. it is a winding of wire which can make it hard to read resistance.the thought is that a few windinds have shorted together lowering the resistance of the total length of wire

    have a dealership test it.
     
  3. tabaka45

    tabaka45 Well-Known Member

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    No Yamaha dealer in town, but maybe an auto shop can measure it.
     
  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    With too low of a resistance you're effectively without a primary coil (the coil acts as if it were a shorter, straight wire). No coil, no (or little) induction. No induction, no high voltage spark (and the potential for TCI damage).
     
    jayrodoh likes this.
  5. tabaka45

    tabaka45 Well-Known Member

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    Well, darn. I guess i’ll try to find some shop that can test the one I have. Just seems like the new one would show more than .6 ohms. The Mastech multimeter should be able to read low ohms. I’ve seen some cheap ones on YouTube that work.
     
  6. Polock

    Polock Well-Known Member

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    i looked that up and if i found the right info, that has one of those little 10mm plugs
    NGK CR7HSA
    i've always found those to be prone to fouling. did you ever try a new plug?
    and
    if the primary resistance is half of what is should be, it will draw twice the current that it should [ohm's law stuff] and that might not be good for the cdi
     
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  7. tabaka45

    tabaka45 Well-Known Member

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    The service manual calls for a NGK C7HSA, but the Suppliment calls for a CR7HSA. I bought a new plug but I just replaced what was there. I’ll have to check it tomorrow. If I can’t find a shop to test the new coil I bought I guess I’ll get another one. When I asked the seller to be sure this was the right coil because the reading was low he just refunded my money. So I’m assuming he has had this come up before. Bummer.
     
  8. Rooster53

    Rooster53 Well-Known Member Premium Member

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    I searched around a bit and everything I found indicated a primary resistance of around .5 ohms.

    Such as this:

    https://www.amazon.com/Yamaha-Ignit...=1-2&keywords=ignition+coil+yamaha+grizzly+80

    Not sure what year you are dealing with, this is for 85 and up.

    This one at grizzlyowners.com has an even lower number, but doesn't give the year.

    http://www.grizzlyowners.com/26-maintenance/4366-specs.html

    And as for a faulty/weak coil with a marginal spark, it has been my experience that they tend to cause issues when under load. The engine will normally idle OK, but try to accelerate hard or sometimes just blipping the throttle will cause a noticeable miss as the spark it too weak to ignite the extra fuel.
     
  9. Polock

    Polock Well-Known Member

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    the second link shows this plug https://www.ngk.com/product.aspx?zpid=9729
    a 12mm plug
    Tabaka shows this one https://www.ngk.com/product.aspx?zpid=9618
    a 10mm plug
    this shows a low resistance for a cdi coil http://mastercircuits.blogspot.com/2012/07/ignition-coil-test.html
    a PW80 shows low resistance http://www.manualsdir.com/manuals/652938/yamaha-pw80.html?page=51&original=1 same ignition...?
    something must have changed through the model years, but was it the ignition system.....
    i'm soooo confused :)
     
  10. MattiThundrrr

    MattiThundrrr Not a guru

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    As soon as I see Rooster has weighed in on electrical threads, I know I'm going to be confused.:confused:
    I bought a multi meter 2 1/2 years ago, just put battery in it and attached the leads for the first time this weekend. Didn't use it, but I set it up... I was electrocuted a couple of times when I was young, and ever since, I'm a useless lump where the dark magic of electrons are involved.
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    CR7HSA is this a resistor plug? if it is it could be part of the problem
     
  12. Polock

    Polock Well-Known Member

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    i guess a multi-meter is like your toilet, ya don't always need it but when you do, your sure glad you have one
     
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