Park the 1977 Ford F-250 in a well-ventilated work area. Open the hood of the truck and secure it in place.
Remove the fuel cap from the gas tank. This will relieve the pressure from the fuel filter, so that the gas does not spray everywhere when you remove the fuel filter from the fuel lines.
Locate the small fuel filter directly beside the carburetor. The small in-line fuel filter has a steel fuel line coming out of one end and a rubber hose coming out of the other end.
Slide a small gas catch container under the fuel filter. Loosen the hex-head nut from the fuel line with the open-end wrench, then remove the steel fuel line from the in-line fuel filter.
Remove the rubber hose from the fuel filter by unscrewing the small clamp from the end of the of the fuel filter, using the flat-head screwdriver. The small clamp holds the rubber hose to the fuel filter.
Pull the fuel filter out of the rubber hose and discard the old fuel filter into the small gas catch container. Wrap the Teflon tape around the threaded end of the fuel filter.
Slide the new in-line fuel filter into the rubber hose and tighten the small clamp with the flat-head screwdriver.
Screw the steel fuel line into the other end of the fuel filter. Tighten the fuel line down with the open end wrench. Remove the catch pan from under the fuel filter.
Install the fuel cap back onto the gas tank. Pump the gas pedal four or five times to prime the small fuel filter with gas, then crank the engine.
Inspect the fuel filter, the steel fuel line and the rubber hose for gas leaks. Turn the engine off and close the hood of the truck.