Obtain fresh fuel. Engine Will Not Start. · Brake pedal not depressed. · Mower Engagement Lever is in ENGAGED position. · Spark plug wire is loose or disconnected. · Improper fuel. · Plugged fuel filter. · Electrical problem - See Electrical Troubleshooting Section. Engine Is Hard To Start. · Carburetor is not adjusted properly. You can almost hear the grass growing as you sit there trying to start up your uncooperative riding mower. This is a guide about John Deere riding mower won' t start.