Your D100 Series Lawn Tractor will not start without proper spark plug care. Be sure to check your spark plugs at the end of each season to make sure the connections and contacts are clear, still good and working properly. Just as importantly, John Deere recommends you change your spark plugs every 50 hours. That’s about once a mowing season. Learn how to change them on your 100 Series Lawn Tractor. Let’s go step by step now. For specific information and more details check your Operator’s Manual.