Deceleration Valve: Description and Operation

Fig. 16 Deceleration spark advance system:

Fig. 19b Air Switching Valve System:

Fig. 18a Coasting Air Valve System:

The deceleration system used on some 1982-84 models includes a coasting air valve system, Fig. 18a. and an air switching valve system, Fig. 19a.
Some 1981-88 models incorporate a deceleration spark advance system, Fig. 16, and/or a dashpot, Fig. 17.
The coasting air valve system and air switching valve system are used to reduce HC emissions during deceleration. The engine speed sensor which controls the solenoid valve, will prevent the coasting air valve or air switching valve from operating at or below a specified engine RPM by opening the solenoid valve. On 1400, 1600 and 2,000 cc engines, the specified engine speed is 1800 RPM (+/- 200 RPM). On 2,600cc engines, the specified engine speed is 1600 RPM (+/- 200 RPM). This is done to prevent poor idling or engine stalling at lower engine speeds. The coasting air valve supplies additional air to the intake manifold at engine speeds within the specified range, from a port located below the secondary throttle valve. The air switching valve supplies additional air to the intake manifold at engine speeds within the specified range, from the idle mixture adjusting screw passage located below the primary throttle valve. The coasting air valve and air switching valve are built into the carburetor.
The deceleration spark advance system consists of an engine speed sensor and a solenoid valve, Fig. 16. During deceleration, ignition timing is advanced by intake manifold vacuum acting upon the distributor vacuum advance unit diaphragm, which is routed through the solenoid valve. At or below a specified engine RPM, the engine speed sensor will activate the solenoid valve, changing vacuum acting upon the distributor vacuum advance unit diaphragm from intake manifold vacuum to carburetor ported vacuum.
On some models a dashpot is used to delay throttle valve closure during deceleration to its normal idle speed position to reduce HC emissions.