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  • #1

    Coil Test

    Group,

    I'm testing a pair of used coils I got off ebay. The the plug caps have rust on the connectors and the temp was 50F. I got 3.2 ohms on primary and 28K ohms on secondary. Both had about the same reading. Are these coils good?
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  • #2
    The Yamaha shop manual lists standard values as follows:
    Primary - 1.5 ohms +/- 10% @ 20 degrees C
    Secondary 15 ohms +/- 20% @ 20 degrees C

    At first glance, your readings look a bit high. I think every coil I have ever put a meter on looked high, and they're all still working just fine.

    As an interesting note, I only just now noticed that the shop manual calls for checking the secondary resistance with the spark plug caps removed and you mentioned some corrosion on the caps. This would be a good opportunity to remove and clean the caps and trim the leads back about a quarter inch or so to get back to clean wire. Try testing this way and see what you get.
    Ken Talbot

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    • #3
      The plug caps are good for 5K, take them off to get a proper secondary reading. The coils on 78-80 bikes have a lower primary resistance than 81 coils. What kind of bike are we talking about?

      Check out the Coil info in the tips section for more great stuff...
      Gary Granger
      Remember, we are the caretakers of mechanical art.
      2013 Suzuki DR650SE, 2009 Kawasaki Concours 1400, 2003 Aprilia RSV Mille Tuono

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      • #4
        Gary,

        It's my 80G.

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        • #5
          Originally posted by Scootstado2
          Gary,

          It's my 80G.
          Kens post above would be the correct values for an 80, except I think he meant 15Kohms not 15 ohms for the secondary. I meant what kind of bike did the donors come from? Anyway take off the caps for a true reading of the coil resistance. Then replace them, only 3 bucks a piece for new caps.

          Caps should be 5K each or 10K plus the 15K is 25K +/- 10% so the are probably close enough (being the caps are crappy) the 3.2 ohm primary is not right for an XS of either type but the after markets have 3 ohm primaries. So they will probably work.

          Please read The Coil FAQ for more info.
          Gary Granger
          Remember, we are the caretakers of mechanical art.
          2013 Suzuki DR650SE, 2009 Kawasaki Concours 1400, 2003 Aprilia RSV Mille Tuono

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          • #6
            Russ,

            Just noticed your avatar..........bahahaha....thanks I needed that !
            Gary Granger
            Remember, we are the caretakers of mechanical art.
            2013 Suzuki DR650SE, 2009 Kawasaki Concours 1400, 2003 Aprilia RSV Mille Tuono

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            • #7
              bad boys, young girls, something about violet?

              Of course Gary is correct about the secondaries being 15K ohms. That was one high school shop class I never did quite figure out...
              Ken Talbot

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              • #8
                Hey Gary,

                I was waiting for someone to get the picture. I thought it might be too small to really tell what it is. That is my head however. The ebay seller said they came off a 80G and they look the same just been out in the weather fotr a number of years.

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