How a Carburetor Works – Float System

How a carburetor works: the float system
Float Circuit

The float circuit includes the float (brass, or nitrophyl), needle & seat, or float valve, bowl vent & float bowl.

The float level and float drop should be measured to insure you get proper fuel amounts. A float that is too high will allow too much fuel into the float bowl and the engine will run too rich. A float level that is too low will not allow enough fuel into the float bowl and a lean condition will result. There will not be enough fuel at high speeds.

The float bowl vent is used to keep the float bowl from becoming a vacuum chamber and in later years is used to vent fuel fumes back to the engine.

The float drop is used to allow the float needle to open and allow fuel to flow into the float bowl. The float needle may, or may not have a clip that attaches the needle to the float. Not all carburetors need this clip. There is usually a measurement to follow for the float drop, but you need to be sure it doesn’t drop so far that it allows the needle to fall out, or get pushed to one side, binding the needle.

Quadrajet Float Pin
Quadrajet Float Pin

Mercarb Float
Mercarb Float
Updated on 04/13/2022

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