When the gas and air flow through the carburetor, they need to have the precise mixture. Otherwise your engine on your Echo line trimmer will perform poorly, slowly and may not even start at all. The carburetor adjustment screws set this mixture, and these screws, located on the engine, can vibrate loose over time. Setting these screws on a regular basis will ensure you keep the proper fuel and air mixture running through the carburetor and engine.
Idle Adjustment Screw
Pull out the air filter. Clean the filter, or replace it if it's too dirty clean. Remove the spark arrestor screen from inside the muffler, and clean or replace it as well if it's too dirty to clean.
Locate the idle adjustment screw on the rear of the engine near the spark plug.
Turn the screw clockwise to increase idle speed; turn it counterclockwise to decrease idle speed.
Watch the trimmer head to make sure it doesn't start moving while the engine is idling. If it does, back off the idle speed.
Low Speed Adjustment Screw
Start the trimmer, and let the engine warm up for a few minutes.
Locate the screw marked "L." This screw is located on the rear of the engine near the spark plug. Turn the screw clockwise so it is all the way in or seated. This is your leanest fuel setting. Turn the screw back one-quarter turn, and remember this setting.
Turn the screw counterclockwise until the engine makes a heavy bubbling noise. This is your richest fuel setting. Turn the screw back one-quarter turn, and remember this setting.
Fine-tune the screw by moving it in between the rich and lean fuel settings. Listen for the cleanest, smoothest sound from your engine. Re-tune the idle speed if necessary.