Champion spark plug (RCJ6Y). The spark plug ignites the fuel and air mixture in the engine's cylinder to power the engine. If the spark plug is has fouled (if the tip of the spark plug is burnt or damaged), the engine may not start or may run rough.
Carburetor for two-cycle engine. If the carburetor is clogged, the engine won't get enough fuel. As a result, the engine may not start or may run rough. The carburetor can often be cleaned or rebuilt, but sometimes it may need to be replaced.