How to know if the spark plug is fouled ?

3 replies to this topic
  • humbertob

Posted January 08, 2002 - 07:04 AM


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 ! :)

  • sirthumpalot

Posted January 08, 2002 - 07:14 AM


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).

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Chris_Slade

Posted January 08, 2002 - 10:21 PM


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!

  • Shawn_Mc

Posted January 10, 2002 - 03:29 PM


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. :)

Related Content


Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Need help by Goforaride

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  68 replies

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

yz400f throttle bog by yz400fmaniac

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • * * * * *
  • Hot  28 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.