Idle Enrichment System: Operation

When vacuum is applied to enrichment valve diaphragm, idle air is reduced enriching the air/fuel mixture. When engine is cold, coolant vacuum switch is open and vacuum is applied to enrichment valve. When engine warms to 98°F, switch closes and engine returns to normal mixture condition.

The solenoid vacuum 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.