Baldrick's Spark Plug Pages
What should they look like?
If it looks like this you're winning. A light brown greyish colour
and nothing out of the ordinary.
Blistering on the insulator, or rounded off melted center electrode.
Ouch! this is hot. Possible causes are a duff cooling system or over advanced ignition timing. If everything else is okay, try a colder grade
plug.
Bloody Hell, must be a 2-stroke!! No seriously, even 2-stroke engines
which rely on an Air-petroil mix wouldn't have plugs looking like this unless there was a
problem. Worn rings or Valve stem oil seals or guides could be the cause. If the ignition
system is playing up then of course the plug could get like this through poor or no
ignition.
Quick call out Dick Van Dyke to sweep up the soot (okay so you don't
know Mary Poppins). If you've tweaked up the mixture to make your machine ' more powerful'
forget it. If not, it's time you checked the mixture or your ignition system. If
everything appears okay, try a hotter grade plug.
Excessive amounts of oil or oil of low quality can cause this to
happen. Clean the plug up or heat damage can occur.
Yes I know it still works but it really is time you bought a new one.
Worn plugs overstress the ignition system and waste fuel. Also increases air pollution.
Images from Haynes Manual
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