Spark dud

[fieldy]

I always see where people say "try a new spark plug first when a motor quits running". I have never replaced a spark plug in any motor and ended up saying "replaced the old spark plug with a new spark plug and it runs now". Yes, i have fouled my share of 2 stroke sparkers, i clean them up and let them naturally dry and they are all fine. If cleaning and waiting didn't cure the plug, I don't remember when it didn't.
I have never had to oven bake any of em, just set them aside and run a different plug for a while. I do not seperate my plugs as older or newer or cleaned. I have never seen one that had an ate up electrode personally. I would think over heating or bad time would be detrimental to a spark plug and cause visable damage. What about invisable malfunctions? Is the only way to check a spark plug by putting the plug in a boot and checking for spark against the cylinder head? Anyone been shocked by testing them? I understand that being shocked by motor can be serious and thinking deadly in some cases.
What will cause a spark plug to go bad? Is it really so common or like one in a million or just mumbo jumbo? I was just thinking about that and wondered if I could pry a story or two out about that plug that went bad. Positive I will learn a few things as always.

[barnett468]

Getting shocked by a plug wire will not harm you in any way because there is not enough amps . . I was shocked by around 700 volts and I'm still here.

[jb2wheels]

I admit it doesn't help very often but twice in my life I spent hours and $$ chasing issues that turned out to be a bad plug.

Once on a 400SBC in a Blazer that had a persistent miss and once on a 70 I could not keep running for more than a few seconds at best.

The 70 would make a spark when set against the head. I have no clue why the plug was bad.
I don't remember the details on the SBC except the thing truck got wet while off-roading. I believe the water ruined the plug.

[YTZ drew]

Sometimes they will fail to spark under compression, due to faulty insulation up inside where you can't see. That's why the old spark plug cleaner/tester machines that auto shops used to have would include a chamber with a glass window that the plug went into, and got pressurized with shop air. Then a transformer inside would energize the plug and you could watch it spark under pressure.

I have cleaned my share of plugs too, usually successfully. I've also had a few just "fail" like you describe. Two of them were Champions, the other might have been an NGK or an ND, but its been a long time.

[oscarmayer]

many reasons they can go bad, from bad manufacturing, to oil contamination. the insulator (ceramic cone) can get saturated and thus all it to ground out instead of spark. the more dirty it gets the less spark it produces hence why we state change the plug. for $2, stop being a cheapass and replace it! :P

[briano]

The only time to clean a plug is in a pinch to get home. I love the people that will buy the top shelf carb cleaner for $6 a can just to use half of it cleaning a spark plug. Then sit and wire brush it, sand the electrodes and reset the gap. So, $3 worth of carb cleaner, 15 minutes farting around, profane in a torch to dry them, and they might work as good as a new one that cost $3. I don't get how some people can be so cheap, but I see it everyday in the auto repair shop I work at.

[83ATC185]

I do like the little sandblaster plug cleaner. I've brought many an XR80 plug back from an oil fouled death with that thing. Had about 10 of them, kept them in a little box right next to the case of off brand 40 weight lol the little thing smoked like tommy chong but it never died. If you have one of those, id say, clean em and run em if its a known good running bike. But if its ever questionable, just replace it. I've spent too much time troubleshooting an ignition system over a spark plug that was bad for unknown reasons.

[YTZ drew]

I haven't cleaned one in years, but I used to do it all the time when I was a kid and would foul plugs on my QA50 Honda. I had no cash, and would have had to bug my mom for a ride to the bike shop, since the parts stores near me didn't have tiny 10mm spark plugs. Someone told me to soak my plugs in vinegar overnight, and thats what I used to do. It actually worked! Cleaning an oily 2-stroke plug may not work as well, but the light carbon fouling that my tiny 50cc 4-stroke would cause came right off. So did the bright cad plating that NGK used, they all turned silver!