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Spark Plug Cap Resistance

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Did you know that spark plug caps have quite a bit of resistance?

I think about 500k.

I figured this out while trying to diagnose a spark problem.

I guess you're never to old to learn something.

So...don't use one from the car!

All plug caps have resistors to minimize electrical interference

But it's not 500K is either 5k or 10K

500K would be a plug cap that is nearly an open circuit

Had the Bultaco M125 out for a run around today. After about 20 minutes it quit running. after checking all normal stuff I checked the plug cap. Now this was a brand new NGK cap and it had 5000k or open. So on goes the old cap back on and the Bully started right up. Never trust a part just because. it's new

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All plug caps have resistors to minimize electrical interference

But it's not 500K is either 5k or 10K

500K would be a plug cap that is nearly an open circuit

Right!

Still getting used that newfangled digital meter!

5k is fairly standard - its used for noise (electrical noise/interference) supression. Should be used with CDI ignition - some of the older points ignitions dont use the resistor.

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