20-05-2021, 10:18 AM
(19-05-2021, 06:25 PM)John Cornforth Wrote: An ohmmeter test is better than nothing, but won't show up electrical leakage/breakdown at high voltage. Capacitors can also develop high internal resistance, which degrades their performance but is not straightforward to measure. Best to carry a spare which you have verified by fitting it to an engine to check that it works OK. This applies to new ones too.
Absolutely correct John, if you have a look at my "Restoring a Top Hat" thread, latest entry, you'll see that I've been having trouble with a condenser. An ohm meter test showed nothing at either normal temperature or when heated with a hot air gun (the ignition was failing after a few miles). I guess that the capacitor was breaking down under voltage stress, becoming progressively short or open circuit after a few minutes running. After not being used for a bit, it "healed" and became operational again.
The quality of some of the new capacitors available causes concern, as you say, best to have a few tested spares under the seat if you are a driver.