The Fuel filter is located in the base tray, just inside service door. Should be rectangular shape, metal silver color, and have two fuel lines attached to it. It is attached to base with bracket. Easiest way to change is to remove two screws holding bracket to base ( 10 mm wrench), pull filter with hoses and bracket still attached out of tray. Fuel lines may then be removed and filter replaced. Be careful to install lines so they dont get kinked and restrict fuel flow, and use good fitting wrenches on line fittings so corners dont get rounded off.
Onan p/n 149-2513, Fleetguard p/n FF-236. NAPA, Carquest, Wix can supply also. Push gen switch to "stop" to run fuel pump when done and check line connections for leaks, and to prime system