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Looking at the spark plug firing tips can tell you if your engine has a problem that needs correcting. They reflect the performance of a well tuned engine or a poorly maintained engine.

Bad spark plugs can cause overheating, rough running, power loss, and even engine failure. Check your spark plugs regularly and use this chart as a guide to spot performance problems.

		1. Normal

		2. Normal with Red Coating Cause: Red coating resulting from fuel additive in unleaded fuel.

		3. Fuel Fouled Cause: Faulty choke--overly rich fuel mixture, ignition problems, or plug heat range too cold.

		4. Detonation Cause: Over-advanced timing, low octane fuel.

		5. Worn Plug Cause: Plug is used beyond its service life. Needs to be replaced.

		6. Carbon Fouled Cause: Plug heat range too cold--extended low speed driving.

		7. Pre-Ignition Cause: Plug heat range too hot--over-advanced timing, air/fuel mixture too lean.

		8. Oil Ash Fouled Cause: Poor oil control--worn rings, worn valve guides, and valve seals.

		9. Mechanical Damage