Examine the square-shaped carburetor, located between the air filter housing and engine block. Examine the round-shaped primer bulb and locate the two screws that secure the bulb retainer plate to the carburetor body. Depending on the specific trimmer model, you may need to remove air filter housing from the carburetor to gain access to the primer bulb screws.
Remove the two screws securing the primer bulb retainer plate to the carburetor body, using a Phillips screwdriver.
Lift the retainer plate from the carburetor, followed by the primer bulb. Remove any residual rubber from the carburetor, using a small flat-head screwdriver and a clean rag, if needed.
Fit the replacement bulb to the carburetor. Seat the retainer plate over the replacement bulb. Secure the retainer plate to the carburetor, using the original screws.
Replace the air filter housing, if necessary.