SOHC.co.uk Forums > CB500/550
First Start Highs and Low!
McCabe-Thiele (Ted):
I don't know how long you have left the ignition on for, I'm not 100% certain but it's very unlikely that both coils would be cooked, only the one where the points were closed possibly.
In the past I've left the ignition on overnight (on a car), the battery was flat, the coil body was hot, when it all cooled down it was OK again.
Neilw:
--- Quote from: McCabe-Thiele (Ted) on October 03, 2026, 08:10:58 PM ---I don't know how long you have left the ignition on for, I'm not 100% certain but it's very unlikely that both coils would be cooked, only the one where the points were closed possibly.
In the past I've left the ignition on overnight (on a car), the battery was flat, the coil body was hot, when it all cooled down it was OK again.
--- End quote ---
It's my best guess, as the regulator is within spec, so it shouldn't have caused the issue. I guess 50-year-old electrics are susceptible; I had to change the solenoid out, as that was also bad.
McCabe-Thiele (Ted):
As a general rule it's moving parts such as solenoids, ignition switches, indicator relays that are common failures.
If the original coills fail it's usually just the HT leads themselves that cause problems.
Oddjob:
It’s well known if you leave the ignition on and the coils energised they are prone to burning out Ted. It’s not common as it requires some time to happen but it does happen now and then. Other than the leads they are almost indestructible.
deltarider:
--- Quote from: Oddjob on October 03, 2026, 11:38:20 PM ---It’s well known if you leave the ignition on and the coils energised they are prone to burning out Ted. It’s not common as it requires some time to happen but it does happen now and then. Other than the leads they are almost indestructible.
--- End quote ---
Not only that. Provided breakerpoints gaps are set within specs, both coils are energised between 1,1 and 4,4 % of the time. So if you're unlucky, both coils will die, when bike is left with the ignition on. ;D
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