Temperature controlled spark advance on vehicles equipped with Hondamatic transmission is designed to reduce NOx emissions by disconnecting the vacuum to the spark advance unit during normal vehicle operation. When the coolant temperature is approximately 120°F (49°C) or higher, the solenoid valve is energized, cutting off vacuum to the advance unit.1975-79 1237cc Air Models
INTAKE AIR TEMPERATURE CONTROLS
Same as 1973-74 models.THROTTLE OPENER
Same as 1973-74 models.TRANSMISSION CONTROLLED SPARK ADVANCE
Same as 1974 models, with no coolant control override.IGNITION TIMING RETARD UNIT
Same as 1973 models, but is used only on Hondamatic models and has no vacuum advance mechanism.