<P> Classic British motorcycles, with side - draft slide - throttle carburetors, used another type of "cold start device", called a "tickler". This is simply a spring - loaded rod that, when depressed, manually pushes the float down and allows excess fuel to fill the float bowl and flood the intake tract . If the "tickler" is held down too long it also floods the outside of the carburetor and the crankcase below, and is therefore a fire hazard . </P> <P> The interactions between each circuit may also be affected by various mechanical or air pressure connections and also by temperature sensitive and electrical components . These are introduced for reasons such as response, fuel efficiency or automobile emissions control . Various air bleeds (often chosen from a precisely calibrated range, similarly to the jets) allow air into various portions of the fuel passages to enhance fuel delivery and vaporization . Extra refinements may be included in the carburetor / manifold combination, such as some form of heating to aid fuel vaporization such as an early fuel evaporator . </P> <P> To ensure a ready mixture, the carburetor has a "float chamber" (or "bowl") that contains a quantity of fuel at near - atmospheric pressure, ready for use . This reservoir is constantly replenished with fuel supplied by a fuel pump . The correct fuel level in the bowl is maintained by means of a float controlling an inlet valve, in a manner very similar to that employed in a cistern (e.g. a toilet tank). As fuel is used up, the float drops, opening the inlet valve and admitting fuel . As the fuel level rises, the float rises and closes the inlet valve . The level of fuel maintained in the float bowl can usually be adjusted, whether by a setscrew or by something crude such as bending the arm to which the float is connected . This is usually a critical adjustment, and the proper adjustment is indicated by lines inscribed into a window on the float bowl, or a measurement of how far the float hangs below the top of the carburetor when disassembled, or similar . Floats can be made of different materials, such as sheet brass soldered into a hollow shape, or of plastic; hollow floats can spring small leaks and plastic floats can eventually become porous and lose their flotation; in either case the float will fail to float, fuel level will be too high, and the engine will not run unless the float is replaced . The valve itself becomes worn on its sides by its motion in its "seat" and will eventually try to close at an angle, and thus fails to shut off the fuel completely; again, this will cause excessive fuel flow and poor engine operation . Conversely, as the fuel evaporates from the float bowl, it leaves sediment, residue, and varnishes behind, which clog the passages and can interfere with the float operation . This is particularly a problem in automobiles operated for only part of the year and left to stand with full float chambers for months at a time; commercial fuel stabilizer additives are available that reduce this problem . </P> <P> The fuel stored in the chamber (bowl) can be a problem in hot climates . If the engine is shut off while hot, the temperature of the fuel will increase, sometimes boiling ("percolation"). This can result in flooding and difficult or impossible restarts while the engine is still warm, a phenomenon known as "heat soak". Heat deflectors and insulating gaskets attempt to minimize this effect . The Carter Thermo - Quad carburetor has float chambers manufactured of insulating plastic (phenolic), said to keep the fuel 20 degrees Fahrenheit (11 degrees Celsius) cooler . </P>

What is the float bowl on a carburetor
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