Ignition-timing adjusting system for spark-ignition internal combustion engines

An ignition timing control system for an internal combustion engine comprising:

• an intake tube for delivering a combustible mixture to an engine and having a vacuum port in the wall of said tube;
• a throttle valve mounted in the intake tube;
• an ignition timing means synchronized with the engine;
• a vacuum actuator having a vacuum chamber and an actuator means connected to the ignition timing means for advancing the ignition timing of the engine in response to increasing vacuum level in the vacuum chamber;
• a vacuum line connecting the vacuum chamber of said actuator to the vacuum port in the intake tube;
• an air line between the vacuum chamber and the atmosphere;
• first valve means in said vacuum line between the vacuum port of the intake tube and the vacuum chamber of the actuator, said first valve means being responsive to the difference in vacuum levels in the intake tube at the vacuum port and in the vacuum chamber of the actuator to open the vacuum line when the level of vacuum at the vacuum port is greater than the level of vacuum in the vacuum chamber and to close the vacuum line when the vacuum level at the vacuum port is less than the vacuum level in the vacuum chamber;
• and
• second valve means in said air line responsive to engine temperature to close the air line when the engine is colder than a predetermined temperature and to open the air line when the engine is warmer than said predetermined temperature, such that the vacuum chamber of the actuator is exposed to the greatest level of vacuum at the vacuum port under all operating load conditions during cold engine operation and to atmospheric pressure when the engine is warmed up.