Editing Carburetor (section)

==Fuel supply==

===Float chamber===
[[File:Holley Visiflo.jpg|thumb|Holley "Visi-Flo" model #1904 carburetors from the 1950s, factory equipped with transparent glass bowls]]
[[File:Carburetor components.png|thumb|A float-type carburetor used in airplanes]]

In order to ensure an adequate supply at all times, carburetors include a reservoir of fuel, called a "float chamber" or "float bowl". Fuel is delivered to the float chamber by a [[Fuel pump (engine)|fuel pump]] or by gravity with the fuel tank located higher than the carburetor. A floating inlet valve regulates the fuel entering the float chamber, assuring a constant level. In some small engines that may instead of a float chamber just use a fuel tank close below the carburetor and use the fuel suction to supply the fuel.

Unlike in a fuel injected engine, the fuel system in a carbureted engine is not pressurized. For engines where the intake air travelling through the carburetor is pressurized (such as where the carburetor is downstream of a [[supercharger]]) the entire carburetor must be contained in an airtight pressurized box to operate.{{citation needed|date=November 2022}} However, this is not necessary where the carburetor is upstream of the supercharger.

Problems of fuel boiling and [[vapor lock]] can occur in carbureted engines, especially in hotter climates. Since the float chamber is located close to the engine, heat from the engine (including for several hours after the engine is shut off) can cause the fuel to heat up to the point of vaporization. This causes air bubbles in the fuel (similar to the air bubbles that necessitate [[brake bleeding]]), which prevents the flow of fuel and is known as 'vapor lock'.

To avoid pressurizing the float chamber, vent tubes allow ambient air to enter and exit the float chamber. These tubes may instead extend into the carburetor air flow prior to where the fuel flows in, in order to use the Venturi effect to achieve suitable pressure difference rather than the Bernoulli principle which applies when the pressure difference is related to the ambient air pressure.

===Diaphragm chamber===
If an engine must be operated when the carburetor is not in an upright orientation (for example in a chainsaw or airplane), a float chamber and gravity activated float valve would not be suitable. Instead, a diaphragm chamber is typically used. This consists of a flexible [[Diaphragm (mechanical device)|diaphragm]] on one side of the fuel chamber, connected to a [[needle valve]] which regulates the fuel entering the chamber. As the flowrate of the air in the chamber (controlled by the throttling valve/butterfly valve) decreases, the diaphragm moves inward (downward), which closes the needle valve to admit less fuel. As the flowrate of the air in the chamber increases, the diaphragm moves outward (upward) which opens the needle valve to admit more fuel, allowing the engine to generate more power. A balanced state is reached which creates a steady fuel reservoir level, that remains constant in any orientation.