The first component of a gas weed eater is the engine, which provides the power necessary to do the work. The engine of a gas weed eater is a simple combustion engine, which works by means of a starting system, a carburetor and an exhaust system. The starting system, which is pull-rope style on weed eaters, causes the spark plug to fire. The carburetor combines carefully controlled amounts of gasoline and air, which are ignited by the perfectly timed ignition of the spark plug. And, the exhaust system carries out the fumes of the burned gas and air.
The action of the engine is converted to working power via a gear system, which varies from one machine to another, but usually consists of a clutch from the engine which connects to a drum. The drum connects to a shaft, which is contained in the pole of the trimmer; the shaft spins via the power from the engine and is attached to the trimmer head.
The trimmer head is where you will see the actual work of weed eating done; it is powered by the shaft, which is moving the power from the engine to the trimmer head. As it receives that power, the trimmer head turns at a very high rate of speed. The line that sticks out from the trimmer head acts like a sharp blade as it meets the stalks of weeds. Some weed eaters are powerful enough to take down small shrubs and branches, but many are designed to handle only your basic weedy type growth.