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Aviation Learning Center Document All About Fuel - P-8740-35
Author: Federal Aviation Administration Date: 2002
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Spark Plug Fouling and How to Avoid It
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In most cases spark plug fouling can be reduced or eliminated by simply applying proven operating techniques. For example, low operating temperatures coupled with rich fuel mixtures result in incomplete vaporization of the tetraethyl lead in the combustion chamber, causing lead fouling of the spark plugs. Maintaining proper cylinder head temperatures will minimize plug fouling problems. In addition:

  • Be certain that maintenance personnel have installed the spark plugs recommended for the particular engine installation.
  • Have the carburetor idle mixture checked and adjusted.
  • Use recommended leaning techniques in cruise condition at all altitudes.
  • Avoid low power letdowns, descend with power, and avoid over-rich conditions. Carburetors and fuel injectors are normally set slightly rich in the closed throttle position, so it is best to carry a slight amount of power on landing approaches rather than approach with closed throttle.
  • Keep the cylinder temperatures in the normal range during operation.
  • After flight or ground operations, before shutdown, advance the throttle to about 1800 RPM for 15 to 20 seconds to clear the plugs and combustion chambers, retard the throttle to about 1200 RPM and shut the engine off immediately with the mixture control. You should not have plug fouling or misfiring on your next startup.

As long as you make sure the aircraft is serviced with the proper fuel, check the sumps for contaminants, operate the engine according to the aircraft owners manual and have the spark plugs serviced as recommended, you should not have plug fouling problems.

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