The more you utilize your Echo string trimmer, the more probable it is that the carburetor will fall out of adjustment, even though it’s factory-set for optimum performance. Combine this with natural wear the spark plug and dirty filters, as well as your trimmer could be functioning at a fraction of its potential. Adjusting the carburetor is a job that you can handle yourself, but do not try to do it by ear. You will need a tachometer to measure engine rank; without it, you can adjust the speed too high and burn out the engine.
General Tune-up Procedures
Run the trimmer until all the fuel is gone, then stop it and replace the fuel filter. It’s on the fuel line in the gas tank, and you can recover the line with a piece of 14-gauge wire formed into a hook. Pull the old filter off the fuel line, push the filter onto the line and drop the filter back in the gas tank, Fill the tank with the proper fuel/oil mix for the own model.
Replace the air filter from closing the choke, unscrewing the wing nut which holds the filter cover and pulling off the cover. Unscrew the spark plug with a spark plug wrench and replace it, but leave the cable disconnected in the plug until after you lubricate the string head.
Clean dirt in the seams. First, remove the spark plug cable and throttle linkage in the carburetor swivel, then unscrew the four screws holding the motor cover, using a screwdriver. Brush dirt off the seams with a stiff paintbrush, then replace the cover along with the carburetor linkage.
Remove the spark arresting screen from behind the muffler by pulling it straight out. Wash the carbon deposits in the screen with a toothbrush; replace the screen if it’s cracked or has holes in it.
Unscrew the deflector in the string head. Loosen the posture screw connecting the trimmer housing into the rotating shaft, then remove the mounting screw and pull on the trimmer casing the shaft off. Lubricate the end of the beam with lithium-based grease, then reassemble the head, housing and deflector.
Adjust the trimmer string so that it’s at its maximum extension. You may either manually stretch the string by pulling it from the head or you can begin the trimmer and tap it to the bottom to automatically advance the string. It must extend as much as the limiting blade on the deflector.
Carburetor Adjustment — Trimmers with Limiting Caps
Connect the spark plug cable to the plug, begin the trimmer allow it to run for five minutes to heat it up. Halt the trimmer and turn the high end screw (“HI”) counterclockwise as far as it will go, using a flat-head screwdriver. Turn the low-speed screw (“LO”) all the way counterclockwise, then all the way clockwise and finally put it midway between those factors. Restart the trimmer.
Set the idle speed by turning the idle screw clockwise until the trimmer head begins turning. Turn the screw counterclockwise until the head stops, then turn it an additional one-quarter turn. Clamp a tachometer onto the spark plug cable; the tachometer must read between 2,400 and 3,200 rpm.
Open the throttle and check for a smooth transition. If the engine stalls, adjust the “LO” screw an additional one-eighth turn counterclockwise and try again. Continue until the transition is smooth.
Open the throttle all the way and adjust the “HI” screw till the reading falls within the specifications listed in your owner’s manual for your model trimmer. This is usually in the neighborhood of 6,800 to 7,500 rpm.
Assess the idle speed and readjust the idle screw, if needed.
Carburetor Adjustment — Trimmer Without Limiting Caps
Start the trimmer and set the idle screw. Turn it clockwise until the head starts spinning, then turn it counterclockwise until the head stops and keep going for an additional one-quarter turn. Halt the trimmer.
Turn both the “LO” and “HI” screws clockwise until they are seated all the way. Turn the “LO” screw one and one-quarter turns counterclockwise along with the “HI” screw two and three-quarters turns counterclockwise. Start the trimmer allow it to warm up for two to three minutes.
Turn the “LO” screw clockwise until the motor begins to race and sputter and notice the position. Turn the screw counterclockwise until the motor again starts to cut out. Set the screw midway between those points, then give it a one-eighth twist in the counterclockwise direction to make the fuel mixture slightly richer.
Clamp a tachometer onto the spark plug cable and open the throttle all the way. Fix the “HI” screw till the reading is within the limits specified in your owner’s manual to your model, which are usually between 6,800 and 7,500 rpm.
Readjust the idle screw after making the high end adjustment.