Fuel Delivery and Air Induction: Description and Operation

OPERATION
Most vehicles use a fuel return system to reduce the possibility of high temperature fuel problems. This system consists of a line connecting an extra nipple on the fuel filter to an extra nipple on the fuel tank sending unit. During normal engine operation, a small amount of fuel returns to the fuel tank. During periods of high underhood temperatures, vaporized fuel is returned to the fuel tank instead of entering the carburetor.

Some vehicles have an in-line check valve in the fuel return system at the fuel filter to eliminate the possibility of fuel feeding back to the carburetor through the fuel return line. This valve uses a stainless steel spring loaded check ball to close the orifice. It is located on the fuel return line and secured by a clamp.