Modern fuel filters prevent many run-time problems that used to plague the mowers of old with their simplistic metal screens. Carburetor float valves are particularly sensitive to rust and grit particles, while small carburetor metering jets may be thrown way out by gummy solids. The paper used in today's filters even limits the passage of water droplets with water's far greater surface tension than gasoline. Replacing the fuel filter periodically is therefore a good way to assure trouble free running of gasoline engines.
Locate the fuel filter. Most fuel systems have a small filter with a semi-transparent housing located on the fuel line between the fuel tank and the carburetor. Visualize it or better yet take a photo and purchase a replacement. Compare the new unit to the existing one carefully before completing the transaction. Sometimes manufacturers change their specifications based on availability and same models and year series may have different filters.
Turn off the fuel tank outlet valve. If it doesn't have one, try to run out all the existing fuel in the tank before replacing the filter, or siphon it out. Barring the above, try to turn the tank to an angle where the line is empty.
Remove the hose clamps from the fuel filter hoses. Depending on the type of mower and its size, this step may require a screwdriver, a nut driver or hose clamp pliers. If the clamps are non-reusable types, purchase new ones with the filter.
Slide the filter out of one hose first, then the other. Carefully note its direction. Note any direction arrows on the filters, and make sure the arrow points towards the carburetor. Also examine the hoses for softening, cuts or nicks.
Slide the clamps on the hoses first if necessary. Slide the new filter into the hoses one at a time. Press the hoses together. Tighten the clamps.
Secure the filter and reinstall or tighten any support brackets. Fill the tank halfway with gasoline, open the valve and look carefully for leaks.
Start the engine, and look for leaks with engine vibrations stressing the joints. If there is a leak, stop the engine, and shut the fuel valve or empty the tank. Repeat steps 2 to 7, but also replace the surrounding fuel hoses and clamps too, available from an auto parts supply.