Holley specs call for a clearance of 0.015-inch. Open the choke and unscrew the idle speed adjuster so that the primary butterflies are fully closed (the fast idle cam cannot hold the throttle open). Turn the carburetor upside down and fully open the throttle. Place a 0.015-inch feeler gauge between the pump cam arm adjusting screw and the pump lever. If there isn't sufficient clearance, tighten the override screw (nut) until the pump lever moves in conjunction with movement on the cam follower arm. If there is too much clearance, loosen the adjusting nut. Remove the feeler gauge, close the throttle, and check the pump cam arm for any play. If any free play exists, the pump cam arm could be bent. The idea is to have 0.015-inch clearance at full throttle and no free play in the pump cam arm when the throttle is closed.