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Testing ignition coils

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Craizeehair:
I have had trouble with the left side not firing a couple of times now, I have carried out some tests that I have found and hoped I could get any informed opinions before I start spending more money on stuff I don’t need.

I have carried out tests on my ignition components as per the Common Motor videos with a test light and I have tested resistance at my coils with my multimeter.

The right side that is sparking had 6.9 ohms across the two wires from the coil and 14k ohms from the plug cap back to the coil.

The left side has 4.3 ohms at the two wires and 14k ohms from the plug cap back to the coil.

Could the left coil be bad? From what I’ve read online, if it has between 3-5ohms it should be ok, any opinions?

There is a disparity between the two, almost a 3 ohm difference but could that be the cause of no spark?

The bike was running on both cylinders until I decided to take the tank off and investigate the hanging idle and erratic tick over??

Bryanj:
4 to 7 is a 50% difference and makes me wonder if one has been changed before

Craizeehair:

--- Quote from: Bryanj on July 12, 2024, 06:24:24 PM ---4 to 7 is a 50% difference and makes me wonder if one has been changed before

--- End quote ---
I did wonder myself, have I missed anything?

I’ve put new plug caps on, cut back the leads for a good connection with them, tried swapping the plugs and tried a new plug but still no spark. Tried bypassing the points and striking a lead on the engine casing to get a spark at the plug but still nothing.

Next logical move is coils… or should I be trying something else?

AshimotoK0:
7 Ohms sounds high .. No resistance figures given in any of my manuals only 'Service Tester' info. I know that Honda 4 cyl.  coils are typically 4.5 Ohm primaries but I will check a Honda twins 12v coil to see whata typical one measures and get back to you. Usually coils reduce in resistance when they are faulty .... if they overheat then turns can get shorted and hence you get reduced resistance across the primary coil.

Craizeehair:
I thought 7 was high based on what I’ve seen online and read, 3-5 seems the norm but that’s the one for me that isn’t sparking and the 7 ohm is.

Does anything else come into play here or have I checked everything I need to and could it come and go if it was on the way out, as it has worked and not worked?

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