Gas weed trimmers keep your lawn and garden looking crisp and beautiful. Using a trimmer often will require adjustments to the carburetor to keep the trimmer running at top performance. The trimmer typically will have three adjustment screws on the back of the engine. The best way to adjust the carburetor is to reset the adjustment screws and start from scratch. The engine will have a chance to burn carbon that builds up within the exhaust as you adjust the carburetor.
Set the weed trimmer upright on the ground, with the head guard on the ground and the bottom of the engine on the ground.
Using a flat-head screwdriver, turn the high- and low-speed adjustment screws clockwise until they fully seat. The high- and low-speed adjustments screws will have an "H" or "L" beside each screw. There also should be an idle-adjustment screw below the two other adjustment screws.
Turn the high and low adjustment screws counter-clockwise one full turn with the screwdriver. This will give you a starting point for the remainder of your carburetor adjustments.
Press the primer bulb three times, and start the weed trimmer. The trimmer should stay running without you pulling the trigger and giving the engine gas. Turn the low-speed adjustment screw counter-clockwise until the trimmer will stay running without you having to pull the trigger.
Hold the gas trigger down, and adjust the high-speed adjustment screw counter-clockwise until the engine will run continuously without hesitation.
Release the trigger, and allow the engine to idle. The trimmer head should not rotate while idling. Turn the idle-adjustment screw counter-clockwise until the engine idles and the head does not move.