The device used to adjust the air/fuel mixture. Usually opposite the throttle arm is the high-speed needle valve. This adjusts the high-speed mixture of the engine and allows you to get peak power from the engine while preventing an over-lean condition. Some newer engines use an angled needle adjustment to keep your fingers at a safe distance from the spinning propeller.
This is used to tune the fuel to air mixture on the engine carburetor. On most engines, the needle is turned clockwise to lean the mixture, and counterclockwise to richen.
The small, tapered male part of a needle and seat.