Air By-Pass Valve

On 1978 Federal B1800, the air by-pass valve is designed to cut off air flow for a few seconds when deceleration mode is first encountered. When throttle drops quickly into a closed position, the by-pass valve will momentarily dump air flow to atmosphere.

On 1979 B2000, the air pump system air passes through by-pass valve to exhaust ports during normal operation. On deceleration, large amount of unburned air/fuel mixture reaches exhaust port area. When by-pass valve manifold connection senses high vacuum level, by-pass valve momentarily diverts part of air pump air back to inlet side of air pump while part is directed into intake manifold to help balance air/fuel mixture during deceleration.