Honda air cleaner (or air filter). If the air filter is clogged or dirty, the engine may not start or may run rough.
NGK spark plug. The spark plug ignites the fuel and air mixture in the cylinder to power the engine. If the spark plug is burnt, fouled or damaged the engine may not start or may run rough.
Lawn mower air cleaner cover. If this cover is cracked, or if one of its holding tabs is broken, replace it.
Small engine carburetor gasket. If the gasket is torn or damaged the engine may run rough.
Small engine governor spring. If the engine does not maintain a consistent speed, then the governor spring may be stretched out or damaged.