How to Set Spark Plug Gaps for a Lawn Mower

Changing spark plugs is part of any lawn mower tune-up. It is also necessary to change spark plugs if an old one is not providing the spark necessary to start the mower. When changing spark plugs, you need to set the spark plug gap for the lawn mower. Too much gap causes backfire in the combustion chamber; too little gap does not provide enough spark to start the engine. It is a good idea to take the old plug when purchasing a new one to ensure you get the correct size for your mower. Recommended plug gaps are often on the back of the spark plug package.

Gap tool

Instructions

- 1
  Read the owner's manual for your lawn mower to find the correct gap for your brand and model, if the gap information is not available on the spark plug package. The maintenance section of your owner's manual or the specifications page usually has this information. Lawn mower engine manufacturers such as Briggs and Stratton and Kohler recommend a gap of 0.030 for new plugs.
- 2
  Insert the gap tool between the ground electrode and the center electrode of the spark plug. The ground electrode is the piece of metal that is bent at an angle over the bottom of the plug. The center electrode is the small electrode coming up through the bottom center of the plug.
- 3
  Adjust the gap tool so that the proper gap thickness gauge is between the two electrodes. If you're using a wire gap tool, the wires around the circumference of the gap tool have a stamp indicating the their gap thickness.
- 4
  Bend the ground electrode up or down as necessary with the notch on the side of the gap tool. Check the gap again and continue making adjustments until the correct gap is set.

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