A carburetor float is that part of a gasoline engine which provides the mixture of
gasoline and air that the engine burns. The carburetor must mix the
gasoline with about 15 times its weight in air for the engine to run
smoothly at all speeds. A driver controls the engine speed by increasing
or reduction the flow of the fuel mixture.
Carburetors are called updraft or downdraft according to their position. If the carburetor is below the intake manifold's input, it is updraft. If it is above, it is a downdraft. The Zenith carburetor, which was used on the Model A, is an updraft.
The float chamber of the carburetor stores a small amount of gasoline, which is gravity-fed from the Model A fuel tank. When the carburetor bowl chamber is filled to the proper level, a float resting on top of the gasoline closes a valve restricting flow from the tank fuel line. As the engine consumes gasoline, the float drops. This opens the valve and lets more gasoline flow into the bowl chamber.
In an extreme case, if the floats are set too high, fuel will overflow via drillings inside the carb body. In addition, fuel may flow into the engine unrestricted, which, if the engine is not running, can cause hydraulic lock – that is, as the piston rises on the compression stroke it cannot compress the fuel.
If fuel is leaking from the carb, it can potentially cause a serious problem – fire. If the fuel height is too high but the bike is running, the engine will have a tendency to display a rich running condition, which will make the throttle response slow and the engine note muffled.
This condition is generally accompanied by a strong smell of unburnt fuel from the muffler. If the fuel height is too low, the engine will display a lean running condition, where the engine typically hesitates before accelerating or surges as the throttle is opened. The bike may also misfire when the throttle is closed.
Carburetors are called updraft or downdraft according to their position. If the carburetor is below the intake manifold's input, it is updraft. If it is above, it is a downdraft. The Zenith carburetor, which was used on the Model A, is an updraft.
The float chamber of the carburetor stores a small amount of gasoline, which is gravity-fed from the Model A fuel tank. When the carburetor bowl chamber is filled to the proper level, a float resting on top of the gasoline closes a valve restricting flow from the tank fuel line. As the engine consumes gasoline, the float drops. This opens the valve and lets more gasoline flow into the bowl chamber.
In an extreme case, if the floats are set too high, fuel will overflow via drillings inside the carb body. In addition, fuel may flow into the engine unrestricted, which, if the engine is not running, can cause hydraulic lock – that is, as the piston rises on the compression stroke it cannot compress the fuel.
If fuel is leaking from the carb, it can potentially cause a serious problem – fire. If the fuel height is too high but the bike is running, the engine will have a tendency to display a rich running condition, which will make the throttle response slow and the engine note muffled.
This condition is generally accompanied by a strong smell of unburnt fuel from the muffler. If the fuel height is too low, the engine will display a lean running condition, where the engine typically hesitates before accelerating or surges as the throttle is opened. The bike may also misfire when the throttle is closed.
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