A riding lawn mower is a major purchase, and keeping it running correctly requires a fair amount of maintenance. Routine service is a bit more complicated than what you get with a push mower. When an issue arises, such as the engine not starting, the problem, again, is compounded by the more complex machinery.
When a riding lawnmower will not start, the first place to start looking for issues is in the fluids. If there is not enough gas or oil in the engine, the machine will not start. Filling the gasoline to the proper level, as indicated in the mower instruction manual, and topping off the oil should solve the issue. The oil and oil filter should be changed after every 50 hours of engine use.
If the fluids of the engine are fine the electrical system may be at fault. Riding lawn mowers require batteries to start the engine. If the battery is not fully charged, or if the wires that connect the battery to the ignition system are broken or faulty, the engine will not start. Batteries will lose their charge over time, but can often be recharged using a special battery recharging tool, which can be purchased from most hardware stores.
Most riding lawn mowers will not start if certain safety features are not engaged properly. Riding lawn mowers often have safety triggers under the seat that keep the mower from starting unless weight is present. If these are not fully engaged, the engine will not turn over. The mower deck often has to be raised on riding lawn mowers so that the blades are not moving before the engine will start. Additionally, many riding mowers have a mower engagement lever that needs to be pulled for the engine to start.
If the clutch on the engine will not engage, the riding mower will not start. Different models have different clutch systems. On a manual clutch system, the clutch pedals needs to be pressed down firmly before the engine will start. If there are any broken wires, the clutch will not engage. Similarly, some mowers have an electrical clutch system that has a small button that needs to be pressed into the "On" position before the clutch will activate the engine. If this part of the electrical system is faulty, the engine will not start.
Along with the safety features and clutch, the brake needs to engage before the mower will start. Some mowers require the parking brake and the foot brake to be engaged simultaneously before the engine will start.