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Needle Valve

Adjustment on a carburetor used to set proper fuel/air mixture. Some carburetors have separate needle adjustments for low and high throttle. Typically, turning the needle clockwise (screwing in) leans the mixture (less fuel), and vice versa. However, there are a few exceptions (refer to the engine manufacturer's instructions).


  • When running an engine in it is best to run it rich - some instructions for two-stroke engines will suggest listening for the engine to four-stroke. This means that the engine will sound as if it is missing now and again.
  • In aircraft installations always adjust the needle setting from behind the propeller and never lean over the propeller whilst doing so.
  • If you have a crash always take care not to rotate the engine or needle valve until you are sure there is no dirt inside the engine or stuck around the needle valve.