SOHC.co.uk Forums > CB500/550

Smoking coil!

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Lobo:
I once killed a ‘750 coil by seeking perfection balancing the carbs on a hot summer’s day. Extended idling / 3000RPM, rising heat, no airflow over the coils..... 4 days later one failed. Bugger.
Bad luck or otherwise I don’t know, but now I stick a fan in front of the bike when tuning it.
Hope no damage done Andy.

andy120t:
Thanks all! Ive checked connections and added an ignition switch. Just waiting for battery to charge up ...on a slow charge at the moment.

deltarider:
Andy, maybe I've missed it: do you have a multimeter and have you measured the resistance of the coils primary and secundary circuit? Original TEC coils should have 4-5Ω primary and 13-15kΩ secundary.
Lobo when your coiled failed, did that occur abruptly or was gradually. Have you measured it?
I ask, because I'm still in the process of finding out if a coil that measures OK, nevertheless can be bad.

andy120t:
I have a multimeter. I checked continuity from battery positive all through to the points gap and there is continuity for both circuits. Should there be continuity all the way back yo the earth lead?

Primary  coil- one side shows 3 and the other shows 6.8 ( this is the one that was smoking). I also have a TEK coil from something which shows 3, as do a the two coils on my 650. So does that mean one is spoilt?

Secondary..don't I need to remove plug caps? I'm a bit unsure of doing that in case I break them.. do they just slip back on?

Battery may also be an issue. I had a new one but its only charging up to 8v do it's going back to be swapped.

K2-K6:
Battery volts at 8 probably won't give you spark at all,  so check again the good coil when you get another.

Looking like that 6.8 tested coil may be unserviceable, either through leaving it on or possibly it was failed before.  Just test your system with new battery with the positive feed for that one apart. Then briefly try it if the other checks out,  but hope for that one diminishes.

Test of HT circuit, yes you need plug leads to have caps removed,  if NGK type they just unscrew to remove and refit.

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