Internal combustion engines

Claim 1

An internal combustion engine having an inlet manifold, a throttle valve for controlling the induction of air into the inlet manifold and fuel metering means for supplying fuel to the engine wherein there is provided a solenoid operated valve for admitting air to the inlet manifold downstream of the throttle valve, the solenoid being energized from an over-run fuel cut-off circuit which comprises a trigger device producing trigger pulses at a repetition rate proportional to engine speed which are fed to a diode pump circuit producing a D.C. voltage proportional to engine speed, said D.C. voltage being fed through a throttle switch, which is closed only when the engine throttle is closed, to a Schmitt trigger circuit producing an output operating a transistor switch to energize the solenoid and thereby opening the valve to admit air to the inlet manifold under over-run conditions, that is when said throttle valve is closed or substantially closed, the supply of fuel is cut off or substantially reduced and the engine speed is substAntially above idling speed.