Fuel filters can be located in a fuel line, in the tank, in a carburetor, or in any combination of these. A carburetor often has a filter behind the fitting at its fuel inlet.
A carburetor inlet filter. Courtesy of General Motors Corporation, Service Technology Group.
Fuel filters that are installed on the outlet side of a fuel pump are called outlet filters.
An external fule filter. Courtesy of General Motors Corporation, Service Technology Group.
Engine heat causes fuel to vaporize, which can result in vapor lock in the filter. Some fuel filters have vapor return lines to allow for expanding vapors and fuel to return to the tank.
A fuel filter with a vapor return outlet. Courtesy of AlliedSignal Automotive Aftermarket.
Fuel injection systems require larger, heavier duty filters than carburetors. They filter out smaller particles of dirt while still allowing the pump to supply a substantial amount of fuel.