DESCRIPTION
Deceleration systems are used to reduce HC emissions. The air switching valve cuts off fuel to by-pass holes and pilot outlet by supplying additional air to slow idle passage. The coasting air valve supplies additional air to intake manifold. The deceleration spark advance system advances ignition timing by changing carburetor ported intake vacuum to intake manifold vacuum.
AIR SWITCHING VALVE
When engine speed sensor detects 1500-2500 RPM, it deactivates air switching valve by opening solenoid valve. This maintains smooth vehicle operation and prevents stalling during change in engine speed.
Air Switching Valve Note flow direction and connections. Scheme 3
COASTING AIR VALVE
When engine speed sensor detects 1500-2500 RPM, it activates a solenoid which deactivates the coasting air valve. This maintains smooth vehicle operation and prevents stalling during change in engine speed.
Coasting Air Valve Note flow direction and connections. Scheme 4
DASHPOT
On all models with manual transmissions (except Federal Pickups), carburetor is equipped with a dashpot. This delays throttle valve closure to its normal idling position, which reduces HC emissions.
DECELERATION SPARK ADVANCE
When engine speed sensor detects 1500-2500 RPM, it activates a solenoid which changes intake manifold vacuum to carburetor ported vacuum, maintaining smooth vehicle operation .
Deceleration Spark Advance System. Scheme 5
With engine idling, push up dashpot free lever to touch dashpot adjusting screw. Turn screw to set idle speed to 1900-2100 RPM.
AIR SWITCHING VALVE SYSTEM
- Run engine at idle. Disconnect solenoid valve connector to disable solenoid valve. Manifold vacuum will act on air switching valve, causing it to open. If idle drops excessively or engine stalls, air switching valve and solenoid valve are okay.
- If idle speed does not change, check condition of air switching and solenoid valves. Also check vacuum passage for clogging.
- With engine idling, battery voltage should be measured at solenoid connector. If no voltage is present, electrical wiring or engine speed sensor is defective.
- Increase engine speed to 1500 RPM. Verify voltage is present at solenoid valve connector. If not, engine speed sensor is defective.
- Increase engine speed to 2500 RPM. Verify no voltage is present at solenoid valve connector. If it is, engine speed sensor is defective.