L-Series Wagon 2WD F4-1781cc 1.8L SOHC (Carb) (1986)
Deceleration Valve: Description and Operation
Fig. 31 Anti-afterburn valve.
During deceleration, high manifold vacuum causes fuel residue on the intake manifold walls to vaporize and be drawn into the combustion chamber.
This excessively rich mixture does not burn completely thereby causing afterburning in the exhaust. The anti-afterburning valve prevents this by
introducing air into the intake manifold to lean the mixture.
During constant-speed operation the valve remains closed since the pressure in chambers A and B, Figs. 31, is the same. During deceleration,
manifold vacuum increases and acts directly on chamber B, forcing the diaphragm down and opening the valve. The open valve allows air to
momentarily be drawn into the intake manifold through the air filter.
The pressure in chamber A gradually decreases to that in chamber B as air flows through the restrictor orifice. This allows the spring to push the
diaphragm up and close the valve stopping the flow of air into the intake manifold.