How to read plugs for a two-stroke

Written by vincent basehart
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How to read plugs for a two-stroke
Your plugs keep a diary of your engine's performance (NA/ Images)

Spark plugs provide vital information about what is happening inside the combustion chambers of your two-stroke engine -- whether it is running rich or lean, hot or cold, whether you should reduce timing or advance it. They may even tell you if your engine needs repair.

You don't need to be a NASCAR pit crewman to learn what your spark plugs are telling you. Learn how to "read" your two-stroke engine's spark plugs to tune your engine for maximum performance.

Skill level:
Moderately Easy

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Things you need

  • Socket wrench
  • Spark plug socket

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  1. 1

    Remove the spark plugs from each cylinder using the socket wrench equipped with the spark plug socket. Keep track of the cylinder from which each plug was removed.

  2. 2

    Observe where the band of colour occurs on the spark plug ground strap. If the band is closer to the bottom of the strap, your engine has too much timing. If it is closer to the tip, your engine has too little.

  3. 3

    Observe the tip of the ground strap. If it is covered with oil deposits, carbon or other debris, the cylinder may be leaking oil.

  4. 4

    Locate the top two threads of the spark plug body, which should have a non-shiny appearance. More than two non-shiny threads means your spark plug or ignition is too hot.

  5. 5

    Look at the porcelain body of the spark plug, which should be a light caramel colour. If it is too white, your engine may be running too rich. If it is too dark, your engine may be running too lean.

  6. 6

    Inspect the tip of the electrode for any dark debris. A clean-running engine will produce a clean spark plug electrode.

Tips and warnings

  • If any of the plugs are fouled and very dirty, you may have an oil leak at that cylinder. Complete repairs on the cylinder before continuing your engine tuning.
  • Spark plugs will be hot to the touch immediately after you remove them from a hot engine.

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