Spark Control System

Fig. 16 Deceleration spark advance system:

Fig. 19b Air Switching Valve System:

Fig. 18a Coasting Air Valve System:

PURPOSE
These deceleration devices decrease HC emissions during vehicle deceleration. The system consists of an Air Switching Valve (ASV), Coasting Air Valve (CAV) and a Deceleration Spark Advance System (DSAS).

OPERATION
During vehicle deceleration;
- The ASV--activated by carburetor ported vacuum--cuts off fuel flow to the by-pass holes and pilot outlet by supplying additional air through the low speed passage to reduce HC emissions.
- The CAV--also activated by carburetor ported vacuum--supplies additional air into the intake manifold.
- The DSAS advances ignition timing, which is usually controlled by carburetor ported vacuum and engine speed.

When the engine speed sensor detects engine speed below 1,300 rpm ASV & CAV operation is interrupted by opening the solenoid valve, to maintain smooth vehicle operation and eliminate engine stall.