Wrench Tip Wednesday: Spark Plugs

Alright, lets show up to a race or play ride day with a bike not wanting to start. Kick and kick, no fire. By the time you start thinking about what is wrong with the bike, you are already physically exhausted. Majority of the time, it is the spark plug.


How important is a spark plug to a dirt bike? A lot of people say they have never fouled one so they do not check or replace it. It all comes down to personal preference on preventative maintenance but realistically it is one of the cheapest things to replace, so why not?


Let’s start with this… Do you know what the purpose of a spark plug is? It fits into the cylinder head and the plugs purpose is create a spark to ignite the fuel. The plug is connected to the ignition coil. NO SPARK = NO START


A spark plug can tell you a lot about how the bike is running by the color.

  • Light grey or light tan means your bike is running well. You can spray contact cleaner on it to clean it up and reinstall.

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  • Carbon fouled has black dry soot on the electrode caused by a dirty air filter, riding at low speeds, bike is too rich, or has been idling too long.
  • Oil fouled has black oily deposits on the electrode caused by oil leaking into the cylinder, finding the source of the leak is important.
  • A wet looking plug is caused by flooding the engine. It can be cleaned and reused.
  • Burned looking, melted electrodes, or white deposits means the bike is running too hot. It can be caused by engine overheating, wrong spark plug, plug being loose, incorrect ignition timing, or the bike is too lean.
  • Worn looking electrodes means the plug has been in the engine too long and is ready to be replaced.

How to change the spark plug:

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Remove the spark plug wires by pulling off the cap, do not tug on the wires because it can damage the connection with your spark plug cap. Make sure you have the correct spark plug socket and attach it to the ratchet. Loosen the plug and finish removing it with your hand. Inspect it and decide if a new plug is needed. Generally, if it is borderline right before a race, we replace it. I know some people still gap their plugs but we do not. We inspect it, make sure it is not damage and install it. Majority of the time they are already pregapped from the manufacture. Go ahead and install the plug, tighten it, and put the plug cap back on.

Being around my dad has made me very particular on a lot of things. It is like everything he has ever taught me just replays in my head, “do this, keep this” and so on. So, I like to keep an extra plug for both my bikes in my van, gear bag, and another in the fanny pack. There is no such thing as being too prepared but being unprepared is common!



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