A riding lawn mower is a large investment, so you want to maintain it properly for maximum efficiency. Regularly checking the fluid levels and performing preventative maintenance on the parts according to the schedule in the owner's manual should keep your mower running. A riding lawn mower or tractor will have troubles occasionally, especially older models, and knowing how to troubleshoot the engine is an essential part of getting the mower running again.
Check the safety switches on the mower if it will not start. An engine will not crank if the safety switches are not depressed properly. Put the lawn mower deck in the correct position and ensure that any safety switches under the seat are depressed.
Check that the battery cables are connected properly. Check that the negative and positive wires are connected to the correct terminal.
Check that the battery is not weak or dead by inspecting the fluid level. Fill lines will be printed on the battery. Wear gloves and eye protection to prevent injury.
Look at the fuses and make sure they are not blown. Replace blown fuses with the specified fuse in the owner's manual, or bring the fuse to a hardware store for identification.
Check that the throttle is in the correct position for starting the mower and make sure there is enough fuel in the tank.
Look at the lines leading to the carburetor, checking for leaks or loose tubing. Connect any loose tubing and replace those that are leaking or cracked.