Ignition timing control system for an internal combustion engine

摘要

Disclosed herein is a system for controlling an ignition timing of an internal combustion engine in its idle condition. A control chamber of a vacuum advancer for operating a distributor of the engine is connected, via a vacuum modulator valve formed as a double diaphragm mechanism, to a vacuum signal port formed in an intake passageway of the engine at a position downstream of a throttle valve in its idle position. The vacuum modulator is adapted to control the vacuum level at the control chamber of the advancer to be reversely proportional to the vacuum level at the vacuum signal port. Accordingly, a stable idle operation of the engine can be obtained.