Tech Support - Spark Plugs Overview

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Tip Temperature and Firing End Appearance

Some factors to consider in selecting the proper heat range spark plug

There are many external influences that can affect the operating temperature of a spark plug.  The following is a brief list to consider in avoiding reduced performance and/or expensive engine damage.

Engine Speed and Load

• If the engine is to be operated at high RPM, under a heavy load, or at high temperatures for long periods a colder heat range may be needed.
• Conversely, if the engine is to be operated at low speeds or at low temperatures for long periods, a hotter heat range might be needed to prevent fouling.

Air-Fuel Mixture

• Excessively rich air-fuel mixtures can cause the plug tip temperatures to decrease and carbon deposits to accumulate, possibly causing fouling and misfires.
• Excessively lean air-fuel mixtures can cause the cylinder and plug temperatures to increase, possibly resulting in knock and/or pre-ignition.  This may cause damage to the spark plug and/or seriously damage the engine.
• If an air-fuel ratio meter or gas analyzer is not available, it will be necessary to visually inspect the spark plugs frequently during the tuning process to determine the proper air-fuel mixture.

Continued...

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