Open the engine cover on the L118 by tilting it forward -- tilt the seat of the L118 upward and set the seat prop. Remove the negative battery cable from the battery, using an open-end wrench to loosen the tie down nut.
Remove the fuel filler lid. Insert the suction end of a pump siphon into the fuel tank. Insert the pump hose of the siphon into a fuel can. Disconnect the fuel pick-up from the fuel line by removing the clip with a Phillips screwdriver.
Pump the siphon until the fuel is removed from the tank completely. If you used a 1-gallon container for bad gas, take the bad fuel immediately to your local shop or auto parts store for disposal. Do not leave the fuel in the container for an extended period of time.
Remove the mounting bolts from the base of the fuel tank with a 3/8-inch drive ratchet and socket. Slide the tank off its base.
Insert the new fuel tank onto the tank base. Install the mounting bolts and tighten them until they are snug. Do not over-tighten the mounting bolts, or you will crack the new tank. Remove the fuel pick-up tube from the old tank, near the fuel filler neck. Install the fuel pick-up tube into the new fuel tank, next to the fill neck. Attach the fuel line onto the fuel pick-up, then tighten the clip snug with a Phillips screwdriver.