How to know if the spark plug is fouled ?

I would like to know when a spark plug is fouled ! What are the symptoms on a bike with a fouled plug, or anything that can tell me the plug is fouled !

Thanks for all your posts ! :)

Sometimes it will start to run pretty bad, typically it will stop running not to long after it starts to foul. A very basic way to tell if a plug is completely fouled is to remove it, put it in the plug cap and ground it to the engine (make sure the silver part of the plug is touching something metal) and give it a quick kick and look for a spark. You should see a clearly visible spark between the center electrode and the piece of metal above it. If there is no spark then it is likely fouled (if you're sure that the rest of the electrical system is OK).


When a bike loses all snappyness to the throttle, loses power, bogs badly, quits, or flat out won't could be fouled.

You can find out for sure by yes, popping the plug. If it is black, it's fouled. 4 stroke plugs can also foul, but be "repaired". WHen a 2 stroke plug fouls, you are screwed, you NEED A NEW PLUG. When a 4 stroke plug fouls, it may not always be black....take some electrical contact/brake cleaner, spray the bottom of the plug good, wipe it off, and give it another spritz. It should look almost good as new...and should run fine then afterwards!

The best way to see if a plug is fouled is to pull the plug cap off and stick a small allen wrench in the cap, hold it in your mouth and have someone kick it with the compression release in. If you feel a "tingle" the ingintion is ok! take out the plug and change it. :)

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