Small engines, the size commonly used in lawn mowers, utilize a carburetor to mix fuel and air in preparation for combustion. Controls in the carburetor control engine speed and are critical for easy starting and smooth operations of the engine and lawn mower. The basic parts are consistent to lawn mower carburetors produced by most manufacturers.
Bowl and Float
Gasoline accumulates in the fuel bowl through a gas line connected to the fuel tank. The float regulates the amount of fuel flowing into the bowl. The bowl and associated float are held in place by brackets usually attached to the block of the engine and are commonly the largest components of the lawn mower carburetor.
Choke and Throttle Plates
These two adjustable plates control the flow of air into the carburetor. The choke plate is partially closed during the start-up process and limits the amount of air flowing into the engine, which creates a richer fuel/air mixture, making the engine easier to start. The throttle plate controls the air flow during normal operations and balances the fuel/air mix to the proper level.
The idle control is commonly a screw on the side of the carburetor. Adjusting this screw controls a valve on the fuel flow associated with the amount of fuel entering the engine at low speed operations. Adjusting this screw raises or lowers the idle speed of the engine and is necessary for the smooth operation of the engine.
Controlling the amount of fuel mixed with the air during normal operations of the lawn mower engine, the needle valve is commonly spring loaded to hold the valve in place.
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