TSB : Normally Open By-Pass Valve (With Vacuum Vent)

Details

With air supply line and vacuum lines disconnected from valve, run engine at 1500 RPM. Air should be felt and heard at valve outlet. Connect unrestricted vacuum line from intake manifold to vacuum source nipple on valve. Little or no air should be felt at valve outlet and virtually all air should be by-passed through silencer ports. Cap the vacuum vent and accelerate the engine to 2000 RPM. Release throttle suddenly. A momentary interruption of air pump supply air should be felt at the valve outlet.