How to Read Spark Plug Colors (written by Atlantic Jet Sports)

In General: Reading spark plugs can be a valuable tuning aid. By examining the spark plug insulator color, an experienced personal watercraft engine tuner can determine valuable information about the engine's overall operating condition.

Normal: Grey to Light Golden-Brown Color

  • This condition is ideal, the spark plug and engine air/fuel mixture are operating properly.

Dry: Black Soot Buildup

  • Air/fuel mixture is too rich, the carburetor settings are incorrect, or the flame arrestor is dirty or has mounting problems.
  • Spark plug heat range is too cold for the operating conditions.
  • Ignition system problems causing a weak or intermittent spark.

Wet Fouling: Shiny, Wet, Black Appearance

  • Excessive use of the choke (gas fouled)
  • Prolonged low rpm operation (gas or oil fouled)
  • Fuel to oil ratio is too rich (oil fouled)

Excess Deposits: Bumpy, Chalky Buildup

  • Poor fuel quality
  • Oil leakage into combustion chamber
  • Improper oil used for premix/injected

Overheated: White, Blistered, Melted Electrode

  • Lean air/fuel mixture
  • Spark plug heat range is too hot for operating condition of the engine
  • Plug is not properly gapped and/or torqued onto head
  • Overly advanced timing

A detonation problem would show signs, such as silver specs, black specs, or melting or breakage at the firing tip.

NOTE: Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and to prevent possible engine damage.

This article was found at www.atlanticjetsports.com