Carbureted Models
The anti-afterburning system prevents the temporary heavy concentration of the air-fuel mixture during rapid deceleration by introducing air into the intake manifold. This prevents afterburning in the exhaust system.
During constant speed running, the valve is closed because pressure in chambers "A" and "B" are equal. During deceleration, with throttle closed, the vacuum pressure in the intake manifold increases and the pressure in chamber "B" decreases. The diaphragm is forced down to open the valve. This permits fresh air to be drawn into the intake manifold through the filter.
After deceleration, pressure in chamber "A" gradually becomes equal to pressure in chamber "B" as air flows through the orifice. The diaphragm is then pushed up by the spring, which closes the valve. See Fig 1 .