Secondary coil readings

[sickpup]

Having problems with one of the Deauvilles.

Intermittent spark failure on the rear cylinder. Coils primary is 2.8 ohms, secondary 196, (might be Kohms, can't remember.) so all within expected parameters.

I've taken the coil off my other Deauville, same model and year which has no spark problems which has 2.9 ohms on the primary and 240 (again might be Kohms) which is 20% over the expected reading.

Both coils are the same part with the same length of HT lead and the same model plug caps.

So oddness aside what effect will a higher resistance in the secondary windings have?

[Easy-X]

Higher resistance usually implies there are more windings (but obviously also depends on wire material and thickness) so one would expect a slightly different output voltage if the coils are built differently. Then again is the peak AC-output of one bike higher than the other
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[A100man]

I'd check those measurements - secondarys are normally in the region of 15-20 KOhms.

Is this a single coils with two outputs - cos then the you have to measure differently..
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[sickpup]

[Fizzer Thou]

Measuring any coil would depend in many instances by the age and condition of the component.Copper wire suffers from skin effect with useage.

The turns ratio of any coil will also differ slightly from one coil to another,even a component that feeds two cylinders like the Honda CD200T Benley that I used to own many years ago.These engines utilise the wasted spark method as is generally known.

The Haynes manuals that I have for for several bikes show the method of measuring the secondary resistance with one of the two multimeter probes shoved into the end of the spark plug cap.The disparity in resistance between two plug caps,even new ones,is quite surprising at times,given that they are specified as being 5,000 ohms on the packaging.Take this factor out of the equation and measure the secondary resistance with the probe inserted into the end of the ignition lead to get the best indication of the circuit.Sometimes there is some corrosion of the copper wire strands so cutting 5mm or so off the end of the lead can make a difference.
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Just talk bikes.What else is there?

Always have a 'Plan B'

[Hong Kong Phooey]

If it's any help at all, the CBR had a low speed stutter. I measured all coils (4x coil on plug) and all primary and secondary winding values were within spec, and all apart from one were quite close to each other in value.

Going off the manual alone wouldn't have helped me much, but I would have thought the odd one out was the faulty.

I bought four used coils and just swapped them all in one go in the end, rather than mucking about, but by process of elimination one of them was dodgy as the bike runs fine ever since.

tldr; you'll probably not know until you swap it, and if it's fine on the new coil just leave well alone and put a new one on, and return the other to its rightful owner.

As for what the higher resistance on the secondary would do, well I thought as the ratio of turns would make the spark voltage higher/lower, so the higher resistance must also have an impact on the final spark output, but if it improves it as you would expect with more windings in the secondary (or in this case, higher difference/ratio between primary and secondary resistances), well I'm not sure.

It might make it weaker in this case, as the same number of turns as before, but the resistance is higher in the 'recieving' circuit, because of degradation. It's frying my brain, hopefully doesn't fry the ECU if there’s also excessive electrical noise.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[Nobby the Bastard]

There are two reasons why a coil would have a higher resistance.

1) thinner wire used on the coil which increases the resistance per unit of length (I'm ignoring different materials)
2) more windings which increase the number of unit lengths of your wire in the coil

I suspect that your more resistive secondary has thinner wire so that more windings can fit in the same space.

More windings will increase the voltage of your spark, which tends to make them more consistant but at the trade of the coil being slightly less reliable because thinner wire melts easier.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[sickpup]

So the other Deauville is almost rebuilt after the coolant problem and has the suspected defective coil on it and misfires so it's safe to assume that it is defective even though all readings are within the expected parameters.