What is a Float Chamber?

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  • Written By: T. L. Childree
  • Edited By: R. Halprin
  • Last Modified Date: 08 November 2019
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A float chamber is used as part of a carburetor system to regulate the amount of fuel being supplied to an engine. It is often referred to as a carburetor bowl. These chambers operate by allowing the fuel within them to lift a hollow float that is connected to a shut-off valve. When a sufficient amount of fuel has entered the float chamber, the float rises and closes the valve. If the fuel level in the chamber becomes too low, the float lowers and reopens the valve. Typical fuel chambers can only be used in carburetors that maintain a horizontal orientation.

In order to operate, an internal combustion engine must maintain a steady supply of fuel. Fuel is typically supplied to this type of engine by either a carburetor or some form of fuel injection. A carburetor-equipped engine must maintain a reservoir of non-pressurized fuel for aspiration into its combustion chambers. This steady supply of non-pressurized fuel is maintained inside of the carburetor’s float chamber.


The float chamber of a typical carburetor contains a hollow float attached to a needle shaped valve. In a normal carburetor configuration, fuel enters the float chamber from a supply line and causes the float to rise to a preset level. When the correct level is reached, the needle valve attached to the float shuts off the supply of incoming fuel. As the carburetor draws fuel from the float chamber, the level decreases and causes a downward movement of the float. This downward movement opens the needle valve and allows additional fuel to enter the chamber.

A different float chamber configuration must be used in non-horizontal carburetors. In this configuration, a flexible diaphragm makes up one side of the chamber. This diaphragm is connected to the needle valve and takes the place of the float. As the engine draws fuel out of the chamber, the changing air pressure moves the diaphragm inward. The inward movement of the diaphragm causes the needle valve to open and replenish the fuel supply.

Engines equipped with a carburetor can sometimes develop problems associated with the float chamber. The brass floats utilized in the chamber will sometimes develop a leak, which causes them to lose their buoyancy. Plastic floats may deteriorate and become too porous to function properly. The formation of float damaging gum and varnish may also occur when fuel is held in the chamber over a period of time. A poorly operating float will usually cause the fuel in the chamber to rise above the correct level and flood the engine.


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