Deceleration Control
A deceleration (gulp) valve is used on AIR systems as an aid in preventing backfires during high vacuum conditions. High manifold vacuum draws deceleration valve diaphragm down and opens valve allowing air from air cleaner to flow into intake manifold. Incoming air leans air/fuel mixture during deceleration.
When throttle valve is closed and engine RPM is high, high manifold vacuum draws an excessive amount of fuel from idle discharge ports. Deceleration valve effectively controls this temporarily rich mixture condition. See Fig 2 .
CAUTION:
When cleaning engine or under hood compartment with steam or high-pressure detergent, mask off intake air filter to prevent liquids from entering pump.