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. On coolant vacuum switch; when engine is cold, switch is open and vacuum is applied to enrichment valve. When engine warms to 98°F, switch closes and engine returns to normal lean mixture condition. On solenoid vacuum valve; switch receives its vacuum signal from a solenoid valve which is operated by an electric timer. Enrichment duration is approximately 35 seconds after engine start or until switch closes at 150°F (98°F on some models). All switches open approximately 12°F below closing temperature.