Due to carbon buildup and a weakened electrode, the spark plug will degrade over time which can prevent the engine from starting. You should inspect the spark plug for damage or wear and you can also use an ignition tester to help determine if the spark plug is defective. Generally, we recommend replacing the spark plug with a new one once a year.
The residue that results from old fuel being left in the tank can create a restriction in the carburetor. This is why you should always use fresh fuel when filling the tank and a fuel stabilizer to help maintain the quality of the fuel. You can try cleaning the carburetor with carburetor cleaner to eliminate the clog. If cleaning is not effective, you can often purchase a carburetor repair kit to replace some of the components or install a new carburetor altogether.
The ignition coil sends voltage to the spark plug while the engine is running. If the ignition coil is malfunctioning, the engine may not start. As with the spark plug, you can use an ignition tester to determine if the ignition coil has failed and will need to be replaced.
If the starter’s recoil spring is broken, the rope won’t be able to recoil onto the pulley, resulting in the engine not starting. Many recoil spring can be replaced individually, but if may be easier to replace the whole recoil starter assembly.
Flywheel key is a small metal piece which fits into the crankshaft and engages with the flywheel. The engine may suddenly stop if the mower blades hit a hard object and the flywheel key will break in half to prevent damage to the engine. If this happens you will need to replace the broken flywheel key with a new one before the engine can be restarted.