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
Normal: Grey to Light Golden-Brown
- This condition is ideal, the spark plug and engine air/fuel mixture are operating
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
- 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