Float System of Classic Cars Carburetor

We have seen how the carburetor draws fuel from a reservoir supply. Here is all about Things you should know about Float System of Classic Cars Carburetor. This supply must be maintained at an almost constant level if the carburetor is to operate properly.

That is, there must always be enough fuel available for the varying amounts of fuel demanded for all engine operating ranges. When we discussed the fuel pump it was explained that there was fuel flow to the carburetor from the pump, only on demand from the carburetor. ( Please consider the previous article ) 

Since fuel in the carburetor float bowl must be maintained at a specified level for correct fuel metering under all driving conditions, let’s look at how this is accomplished.


Things you should know about Float System of Classic Cars Carburetor

Things you should know about Float System of Classic Cars Carburetor

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Float System of Classic Cars Carburetor

The float system accomplishes this by using a float or hollow can which floats on top of the fuel and exerts force against a needle valve.  Thus it can shut off fuel flow into the bowl when the specified level is reached. 

Fuel from the fuel pump enters into the float bowl through the orifice or opening in the fuel inlet (needle valve).  As the level in the bowl rises, the buoyant action of the float raises the float, which, in turn, seats the needle in the valve seat, stopping the fuel flow.

When fuel is being used from the bowl, the float drops enough to allow the needle to be unseated and fuel will enter past the needle to maintain the level in the float bowl.

The fuel level controlled by the float setting is an important part of the calibration of the carburetor.


If the liquid level is lower than specified, greater than normal air flow will be required through the venturi to lift a given amount of fuel from the float bowl, so the mixture will be lean.


The effects of a lowered fuel level causes poor performance in the main metering system and a definite loss of power.

High fuel level can result in premature main metering delivery and fuel spillage during normal car maneuvering, each of which causes excessive fuel consumption and an over rich condition.

The effects of poor main metering will be better understood when this system is discussed.

The float system is perhaps one of the most important systems in the carburetor, as the correct operation of all other systems depends on a fixed level of fuel in the float bowl.

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Article Source : This article courtesy should goes to Auto Mechanics Autodology – Technical instruction manual by System Operation Support.