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Adjusting Idle Mixtures

Adjusting Idle Mixtures

  • Excessively rich or lean idle mixtures result in incomplete combustion within the engine cylinder, with resultant
  • formation of carbon deposits on the spark plugs and subsequent spark plug fouling.
  •  In addition, excessively rich or lean idle mixtures make it necessary to taxi at high idle speeds with resultant fast taxi speeds and excessive brake wear.
  • Each engine must have the carburetor idle mixture tailored for the particular engine and installation if best
operation is to be obtained.
  • Engines that are properly adjusted, insofar as valve operation, cylinder compression, ignition, and carburetor idle mixture is concerned, idle at the prescribed rpm for indefinite periods without loading up, overheating, or spark plug fouling.
  •  If an engine does not respond to idle mixture adjustment with the resultant stable idling characteristics previously outlined, some other phase of engine operation is not correct. In such cases, determine and correct the cause of the difficulty.
  • Before checking the idle mixture on any engine, warm up the engine until oil and cylinder head temperatures are
  • normal. Keep the propeller control in the increased rpm setting throughout the entire process of warming up the engine.
  • Always make idle mixture adjustments with cylinder head temperatures at normal values. The idle mixture adjustment is made on the idle mixture fuel control valve.

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