Close and securely latch the screen door. Turn the adjustment screw on the end of the door piston body a quarter turn clockwise with a Phillips-head screwdriver. The adjustment screw is on the end of the piston body that connects to the door bracket.
Open the door fully, and allow it to close on its own. Turn the screw another quarter turn clockwise if it still closes too fast and retest.
Swing the door to the half-open position, if the closing speed is still too fast. Slide the hold-open washer over the shaft and against the rear body of the closer to keep the door open.
Grab the door piston body with one hand, and pull the pin out of the front piston and door bracket with your free hand. Move the front of the piston to the next hole closest to it on the door bracket and reinsert the holding pin. Gently open the screen door slightly and slide the hold-open washer back against the piston rod jamb bracket.
Operate the door and allow it to close on its own. Continue making adjustments to the screw in quarter-turn increments until the door closes at a slower rate and still latches on its own.