Idle Enrichment System: Operation

When vacuum is applied to enrichment valve diaphragm, idle air is reduced. As a result of less idle air, air/fuel mixture is enriched.

With coolant vacuum switch, when engine is cold, the switch is open and vacuum is applied to enrichment valve. When engine warms to 98°F (37°C), switch closes and engine returns to normal lean mixture condition.

With solenoid vacuum switch, the switch receives its vacuum signal from a solenoid valve, operated by an electric timer. Enrichment duration is approximately 35 seconds after engine start, or until switch closes at 150°F (66°C); or 98°F (37°C) on some models. All switches open approximately 12°F below closing temperature.