Re: Rough Running Breakdown/recovery!
Posted: Sun Sep 10, 2023 9:15 pm
Stuart often I have come across owners who had their capacitor tested by a knowledgeable friend who is a professional expert with various qualifications who clearly have no real understanding of how an ignition system works let alone the role of the capacitor.
The result is that they have tested it on an Avo or more advanced digital meter and find it satisfactory as it is not short circuited.
By now I have tested many hundreds of capacitors and never found one that is approaching a short circuit. As the back EMF in the primary coil is about 300v this sort of voltage must be used when testing the capacitor.
Automotive distributor capacitors are generally rated at 500v so I use Megger type insulation tester. There is coverage in my article. Virtually all such capacitors are 0.2mfd so choose a new one that can be jiggled to fit in there. Don't buy a NOS one it will be most likely defective by now as they fail with age even if unused.
The result is that they have tested it on an Avo or more advanced digital meter and find it satisfactory as it is not short circuited.
By now I have tested many hundreds of capacitors and never found one that is approaching a short circuit. As the back EMF in the primary coil is about 300v this sort of voltage must be used when testing the capacitor.
Automotive distributor capacitors are generally rated at 500v so I use Megger type insulation tester. There is coverage in my article. Virtually all such capacitors are 0.2mfd so choose a new one that can be jiggled to fit in there. Don't buy a NOS one it will be most likely defective by now as they fail with age even if unused.