Internal combustion engine

A spark timing control system for internal combustion engines, comprising

• a distributor,
• a vacuum means operatively connected to said distributor for actuation of the latter to advance and retard spark timing,
• said vacuum means including an operative spark retard chamber,
• a carburetor intake passageway,
• a throttle valve closeably and openably mounted in said intake passageway defining a vacuum side and an atmospheric side, respectively,
• conduit means connecting said intake passageway with said spark retard chamber of said vacuum means,
• said conduit means communicating with said intake passageway at the vacuum side of said throttle valve when said throttle valve is closed in an idle position and communicating at the atmospheric side of said throttle valve when said throttle valve is partly opened,
• valve means disposed in said conduit means intermediate said intake passageway and said spark retard chamber for selectively communicating said intake passageway with said spark retard chamber constituting a communicating condition and for venting said conduit means constituting a venting condition, respectively,
• a solenoid means for operating said valve means in response to a predetermined signal to change said valve means over from said communicating condition to said venting condition,
• switching means for supplying said predetermined signal to said solenoid means for said venting condition in response to a switching signal,
• said switching means comprises a transistor circuit,
• means for supplying said switching signal to said switching means comprising a comparator circuit and a delay circuit, the latter being connected operatively to said comparator circuit and to said transistor circuit,
• said delay circuit comprises a diode and a first resistor connected to each other, the latter connected to an input of said transistor circuit, as well as a capacitor and a second resistor connected to each other in series, one end of said second resistor being connected at a point between said diode and said first resistor,
• said comparator circuit includes a normally closed switch and a third resistor connected to each other at a junction, the latter being connected to a free side of a diode, as well as an engine speed sensor means for opening said normally closed switch when the engine speed exceeds said predetermined level,
• means for supplying a potential to said transistor circuit, said delay circuit and to said comparator circuit.