The spark plug gap is an area of open space between the two electrodes of the spark plug. Proper distance for this gap ensures the plug fires at the right time to prevent fouling and early ignition of the lawn mower engine.
Manufacturers design small engines to operate using different spark plug gaps. Two mowers from the same company may operate with a different gap. According to Briggs and Stratton, the owner's manual for each device provides the information on the type of plug to use and the gap setting to use with it.
Manufacturers pre-gap plugs to the specifications set for most small engines using them. However, being bumped during transit can sometimes affect the gap. Some engines that require a specific plug need a different gap than what is preset at the factory. Setting the plug involves the use of a wire feeler gauge. Choose the wire on the gauge according to the size of the gap the manufacturer specifies. Adjust the electrodes so the wire moves through the gap with a slight resistance. The tool includes a hook that allows users to widen the gap if necessary. If the gap is too wide, close it by pressing against a soft surface. Make small adjustments and check with the wire to ensure the correct distance.