Many of the problems you encounter while using a Troy-Bilt weed trimmer can be attributed to a dirty air filter, a bad spark plug or a poorly adjusted carburetor. Some of the problems they can cause include the trimmer not idling properly, the engine not starting and the engine stalling while in use. Fortunately, cleaning the filter, replacing the plug and adjusting the carburetor are all things you can do on your own.
Clean the Air Filter
Step 1: Remove the Filter
Set the choke lever to "Position 2" and use a flat blade or T20 Torx screwdriver to unscrew the four screws keeping the air filter cover in place. Remove the air filter cover from the engine. Do not force the cover off, to avoid damage to the cover or engine. Turn the cover over and remove the air filter.
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Step 2: Wash It With Soap and Water
Use water and detergent to wash the air filter. Once the filter is washed, squeeze it to remove any excess water. Allow the filter to dry. If the filter is too dirty to clean, replace it.
Step 3: Lightly Oil It and Replace It
Add just enough SAE 30 oil to lightly coat the filter, and then squeeze the filter to ensure that the entire filter is covered. Place the air filter back into the cover, and then put the cover back in place on the engine. Tightly screw the four screws to secure the cover.
Clean the Spark Plug
Step 1: Remove the Spark Plug Wire
Wait for the trimmer's engine to cool. Once the engine is cool, find the spark plug on the trimmer's cylinder head. Grasp the spark plug wire and pull it to remove it from the spark plug.
Step 2: Unscrew and Remove the Plug
Use a cloth to clean the area around the spark plug. Use a 5/8-inch spark plug wrench to turn the spark plug counterclockwise, until the plug comes off.
Step 3: Set the Gap
Use a feeler gauge to set the replacement plug's terminal gap to 0.020 inches.
Step 4: Replace the Plug
Place the new plug on the cylinder head and use the spark plug wrench to turn the plug clockwise, until it is securely in place. Take care not to tighten it too much. Replace the spark plug wire by pushing it onto the plug until it snaps in place.
Adjust the Carburetor
Step 1: Warm Up the Engine
Start the trimmer's engine and run it at a high idle to allow it to warm up.
Step 2: Adjust the Idle Setting
Let the trimmer's throttle go. If the engine stops, use a #1 Phillips screwdriver to adjust the idle speed screw in the air filter cover. Turn the screw 1/8 of a turn in a clockwise direction to make the engine run leaner. This should increase the idle speed. If the engine slows down, turn the screw in the opposite direction.
Step 3: Fine-Tune the Idle
Start the engine and then release the throttle. If the engine stops again, turn the screw another 1/8 of a turn. Repeat this process until the engine runs idle instead of stopping.
You can make two other carburetor adjustments, using the low-speed and high-speed adjustment screws. Consult the manual for your model to make sure you do this correctly, because a misadjustment of the high-speed screw can damage the engine.