Marine propulsion unit having ignition interruption means to assist

Abstract

Ignition pulses derived from an engine ignition coil primary are fed to the input of an ignition interruption circuit that employs an integrated circuit timer. The state of the output terminal of the timer is governed by an RC time constant circuit and by trigger signals supplied by a trigger circuit in response to occurrence of each ignition pulse. The timer output is coupled to the gate of an SCR which when it receives gate current as a result of the timer output being in a high state becomes conductive and bypasses ignition pulses to ground to thereby lower engine rpm to a preset minimum in which case gate current is removed and at least enough ignition pulses are allowed to be unbypassed for keeping the engine running above stalling speed. The timer, in effect, compares the interval between pulses with its time constant. When the intervals are longer than the time constant period the timer output remains low and provides no gate current, but when the opposite condition exists gate current is supplied until the intervals between ignition pulses equal or exceed the time constant period.