If a weed trimmer seems to run on low power, or its blades seem to run weaker than usual, the engine's spark plugs may be broken and require replacement. Exhaust buildup on the muffler screen also can result in lack of weed trimmer power.
A weed trimmer with a smoking engine can result from a clogged filter. Remove and check the filter for dirt, fuel deposits or other sediment. Cleaning the dirty filter should restore proper weed trimmer engine function.
If a weed trimmer's engine dies, the carburetor, which controls the fuel and air ratio of the engine combustion mixture, may require adjustment. Adjusting the high-speed and low-speed carburetor screws as indicated in the weed trimmer manual typically corrects the fuel and air ratio, and restores engine function.