Ideally you want to adjust the carburetor with the aid of a tachometer. Unfortunately, not every home garage has a tachometer available. You can adjust the speed without a tachometer effectively. Before you attempt to adjust the carburetor, it is a good idea to clean the air filter and the spark arrestor screen first. Many issues that you may think are attributed to the carburetor are often a result of dirty filters and screens. If cleaning the screen and filter does not solve your engine problems, there are three adjustments you can make to the carburetor on your Echo line trimmer.
Locate the three carburetor adjustment screws on your Echo line trimmer. They are usually found around the area where the primer bulb attaches to the carburetor. Each screw will have a letter beside the screw. The high speed screw has an "H", the low speed screw has an "L" and the idle speed will have an "I."
Start the trimmer and allow the engine to run for several minutes. Bump the head to feed the line so that you are adjusting the carburetor with new line to the cut off knife of the head.
Stop the engine and turn the high speed adjustment screw counter-clockwise with a flathead screwdriver until the screw stops. Turn the low speed screw counter-clockwise until it stops and then clockwise until it stops. Determine the midway point and adjust the screw to the midway point.
Start the trimmer engine again and turn the idle adjustment screw clockwise until the trimmer head begins to rotate. Turn the idle screw counter-clockwise until the timmer head stops rotating. Turn the idle screw counter-clockwise once more ¼-turn.
Squeeze the throttle trigger to accelerate the engine to full throttle for 3-seconds. Release the trigger and then slowly squeeze the trigger again to bring the engine to full throttle. If the engine hesitates during acceleration, adjust the low speed screw counter-clockwise in 1/8-turn increments. Continue checking the acceleration and continue adjusting until the engine accelerates without hesitation.
Squeeze the trigger and hold to keep the engine running at full throttle. Slowly turn the high speed screw clockwise until the engine begins to run rough. Turn the screw counter-clockwise when the engine begins to run smooth. Turn the high speed adjustment screw counter-clockwise one more ¼-turn.