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Ignition Coil Windings Resistance 1978 GS750

  • Thread starter Thread starter WDHewson
  • Start date Start date
W

WDHewson

Guest
Hello.

I think there's been lots written about setting ignition timing and measuring ignition coil resistance. But here's my 2 cent contribution.

I set the points up statically (0.018 inch gaps) so that the timing marks lined up to within the width of the F line. So this seems accurate to about 1 deg of advance.

Kicked her over with the plugs out laying on the head, and all cylinders sparked.

But wanted to check the coils for primary and HT resistance. The coil for cyls 1 and 4 was 4.1 ohms primary and 22.5 kohms secondary. For clys 2 and 3 the coil's numbers were 4.1 ohms and 22.3 kohms.

I can't find a spec in the factory service manual, but these numbers seem about correct from what I've found in this forum.
 

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Coils that measure 4.1 Ohms primary resistance are typically called 3 Ohm coils for some reason. The primary and secondary resistance you are measuring seems right.
 
geol said:
Coils that measure 4.1 Ohms primary resistance are typically called 3 Ohm coils for some reason. The primary and secondary resistance you are measuring seems right.
Click to expand...

Thanks geol. I forgot to mention that the two spark plug caps were included in my HT resistance measurements. I don't know if these are resistor caps, and if so, their resistance values.
 
geol said:
Coils that measure 4.1 Ohms primary resistance are typically called 3 Ohm coils for some reason. The primary and secondary resistance you are measuring seems right.
Click to expand...
I've measured six sets of early 1980 ish suzuki coils- all measured about 4 ohms primary and 12000 ohm secondary (wire to wire plug caps removed). I call these 4 ohm coils. Dyna and others make 3 ohm coils for their different ignition system.
 
I found distinct differences on the ones I encountered.
OEM points coils - 4 ohms or thereabouts - not critical, as it's quite stone-age tech.
OEM electronic ign coils - 3 ohms as an absolute minimum iirc.
There's a tolerance of +/- 15% on all of those, anyway.


Don't know where the errors arose - it's as clear as day.

As long as you keep in mind the differences, you can swap them around - for example, I have CBR1000 coils (3ohm) on mine, running perfectly well. There's also a couple of sets of OEM 4ohm coils that work fine with the aftermarket ignitions systems I have - but those systems will tolerate the 3ohm coils too.
 
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Does everyone "zero" their ohmmeters first? I can never tell.... as in touch leads together, note value displayed, and subtract from reading. My shop beater meter usually zeroes at 2.8 so if I was testing resistance on something that " read " at say 10 ohms, I'd say it was really 7.2 ohms.
 
Gorminrider said:
Does everyone "zero" their ohmmeters first? I can never tell.... as in touch leads together, note value displayed, and subtract from reading. My shop beater meter usually zeroes at 2.8 so if I was testing resistance on something that " read " at say 10 ohms, I'd say it was really 7.2 ohms.
Click to expand...

Whenever I use an analogue meter I have the automatic zero-ing habit ingrained from years ago. I only sometimes remember to do it with the DVMs, but only one of them is a drifter as the battery gets lower anyway and that one isn't used for anything important.
 
tom203 said:
I've measured six sets of early 1980 ish suzuki coils- all measured about 4 ohms primary and 12000 ohm secondary (wire to wire plug caps removed). I call these 4 ohm coils. Dyna and others make 3 ohm coils for their different ignition system.
Click to expand...

Thanks tom302.

That's reassuring that the primaries were all near 4 ohms on all your samples.

Rightly or wrongly, I have in mind that a resistor cap is about 5 kohms, so two caps in series adds 10 kohm. Add the cap's 10 kohm to you 12 kohm and you get 22 kohm, which is what I got cap to cap.
 
Gorminrider said:
Does everyone "zero" their ohmmeters first? I can never tell.... as in touch leads together, note value displayed, and subtract from reading. My shop beater meter usually zeroes at 2.8 so if I was testing resistance on something that " read " at say 10 ohms, I'd say it was really 7.2 ohms.
Click to expand...

Thanks Gorminirider.

If you meter's internal's are OK, then you've got 2.8 ohms in the leads, which is way too much. My leads have leas than 0.1 ohm.
 
indeed! and they vary when I wiggle them! :) ... I just wanted to make the point. It makes such a huge difference in low resistance circuits.
 
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