As a part of either routine maintenance, or when your riding lawn mower begins to lose power, miss or perform less than satisfactorily, it is time to replace the spark plugs. Depending on what type of engine you have, it will either be a single-cylinder engine, which uses only one spark plug, or a double-cylinder engine, which will have two. Changing either one or two spark plugs will require the same tools and technique for each one.
Allow the engine to cool if it has been previously running, and pull up the hood of the rider.
Locate the spark plug wire(s), which will be contained within a thick, black and rubber-coated terminus. Each will attach to the spark plug with what is called "the boot." This is the heavy rubber addition to the wire that will completely cover the top of the spark plug.
Remove the boot from the wire by pulling back firmly. You may have to wiggle the boot slightly to dislodge it from the top of the spark plug.
Select the correct socket adapter that fits on the plug that you have. Trial and error works best, unless you know for a fact which socket fits.
Push the socket firmly onto and over the top of the plug, and hand-turn slightly to seat the socket.
Attach the ratchet head to the socket and begin to turn it in a counterclockwise rotation. It may take a bit of muscle at first to free the plug on the first turn.
Turn counterclockwise until the plug loosens and can be removed.
Hand-thread a new plug into the open hole, turning it in a clockwise rotation until it becomes difficult to turn. Attach the socket to the plug, and tighten it up with the ratchet, seating it firmly back into the engine.
Push the boot back onto the spark plug top and repeat the procedures above if you need to change more than one plug.