Poulan trimmers allow the operator to change the idle speed setting, which regulates the engine speed. The ideal idle setting is the maximum speed before the head starts to rotate without pressing the trigger. For this reason, you will need to keep people and pets clear during this procedure, as the head will spin while you adjust the carburetor. After you make the adjustments you will need to continue monitoring the head to ensure it doesn't spin while idling.
Start the Poulan trimmer and depress the throttle trigger for a few minutes to warm up the engine. Hold the front handle with your left hand while making the adjustments with your right hand.
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Locate the idle speed adjustment screw, which is between the air filter and the starter handle on the carburetor. Insert the screwdriver into the idle adjusting screw.
Turn the screw clockwise until the head starts to rotate. Turn the screw back counterclockwise 1/8 of a turn or until the head stops spinning. Depress the throttle and let the engine run for a minute. Let go of the trigger and allow the head to return to an idle. Make adjustments to the idle screw if the head still spins or the engine dies.