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Coil?

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Martin6:
Hi,
Please, could someone direct me to, or run me through the check for CB750K coils? I think I've read somewhere of some resistance specs that can show a damaged coil?

I guess I could swap them over, but I'd prefer not to disrupt the connections on 1&4.

My 750K6 has suddenly started firing on 1 & 4 only. I have checked the points and no current when 2 & 3 points opens. I've traced the wiring and connectors which look OK, even nipped 1/2" off the end of the HT leads, just in case.

Was running fine at the weekend. The only thing I can think is I'd noticed my horn had stopped working. I looked at it today and traced it to the handlebar switch, cleaned everything and resolved it. I'm wondering if my on/off testing for the horn might have fried the coil, because I forgot to turn off the kill switch!

Thanks, Martin

K2-K6:
Worthwhile checking supply to tbe coil first as may have been disturbed during fault finding.

The two wires to points are the earth route from coils that are switched to make it spark.

In addition, you'll have each coil fed with positive coming into the coil. Check that first to see if its not available on 2/3 coil as that would make that set completely dead right down through the points.

Unusual to damage the coils easily, so wouldn't be initially concerned about that possibility.

Bryanj:
Black and white leads at coil(s) should have 12v to earth with ignition on and kill switch on.
Disconnect blue and yellow wires and should be 12v between COIL contact yellow and blue to earth.
If so problem is on wires to points or on points themselves

Martin6:
I didn't have the tank off for the horn issue, so didn't disturb the coil feeds. Subsequently, I did remove the tank to check the coil's leads and connectors visually and all looks OK. I'll do the voltage checks tomorrow.

What I did notice is both rubber grommets on the HT leads at the coil look cracked and perished. I did wash the bike after my last ride, so water may have got into the coil?

Thanks.

K2-K6:
Quite possible from water ingress, but likely if it's anything near or around HT to be functioning with it tracking out somewhere to find earth other than the correct route via plug. That would be quite common an occurrence and so valid to check there too. Hairdryer and then silicone grease to prevent further ingress may give results.

If you started it in the dark then you'd see that flashing across to something nearby, probably here a "crack" as it did so too, but a little close to engine noise to discern.

Initially though, without a supply into the coil being verified, then its difficult to judge conclusively as to where the fault may originate.

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