Air Valve Spring

Using an Allen wrench, loosen lock screw. Turn tension adjusting screw counterclockwise until air valve opens part way. See Fig 1.
Turn tension adjusting screw clockwise until air valve just closes. Then turn adjusting screw clockwise specified number of turns.
Hold adjusting screw and tighten lock screw.

Fig 1: Air Valve Spring Adjustment
Courtesy of GENERAL MOTORS COMPANY

Tighten adjusting screw specified number of turns.