Ignition coil question


XS400 Member
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Northern Virginia
Forgive me because this is my first ever motorcycle and I'm no Mechanic.

I have a 1980 XS400 Special and I tested the ignition coils. According to the Haynes manual, the primary resistance range should be between 3-5 ohms. Mine measure 2.6. The secondary resistance range should be 10.0 and above....mine measure 8.26 and 8.29. So my assumption is that I need to replace the coils. I was reading this thread and this gentleman gives the same measurements of his coils and seems to imply that those readings are normal. No one advised him to replace them or even suggested that he troubleshoot them.

So, I bought two coils off of eBay and measured them when they arrived and they have the same measurements as my existing coils and the coils from the thread above. Am I missing something here? Are all three sets of these coils bad or are they all good and I didn't need to replace mine? I could use some direction.
The specs for your bike from the factory manual are:
Primary resistance should be 3.0 ohms +/- 10% at 68 degrees F (so, 2.7 to 3.3 ohms).
Secondary resistance should be 8.6k ohms +/- 20% at 68 degrees F (so, 6.88k to 10.32k ohms)

It looks like you are out of spec low on both (I think your secondary measurements are meant to be in k ohms, if so, your secondary measurements look fine.)
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I though about this overnight - it has been pretty cold outside lately and your primary readings are pretty close to good. I would bring your coils inside and clean up the outside of the coil and the primary wire plug and wires. A little dish soap, water and an old toothbrush works great for this, just don't dunk the coils in water. Sometimes a bit of dirt and grease can cause paths for current flow and affect your readings. Then, keep your coils inside for 24 hours so that they warm up to room temperature and re-take the readings.

I think your coils are probably just fine to use.