Two cycle engine carburetor. If the engine runs rough, the carburetor may be restricted. The carburetor can often be cleaned or rebuilt, but sometimes it may need to be replaced.
Champion Spark Plug (RDJ7Y). 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.
Small engine carburetor gasket. If the gasket is torn or damaged the engine may run rough.
Fuel tank assembly
String trimmer bump knob assembly.