Abstract: A pole-shoe magnet group assembly for a magnetomotive device such as a magneto for the ignition system of an internal combustion engine. The group carried by the rotor includes a permanent magnet and a pair of pole-shoes extending generally circumferentially from the magnet in opposite directions. A coil/core group for electromagnetic cooperation with the pole-shoe magnet group is disposed on the stator. The inner surface of each pole-shoe is defined by a circular arc having a center eccentric to the center of rotation of the rotor. The inner surfaces of the pole-shoes and the core of the trigger coil define an air gap or spacing which varies during rotation of each shoe relative to the core. The signal induced in the trigger coil by this construction inhibits unwanted firing of a solid state switching component and in a breakerless ignition in response to reverse rotation of the magnet pole-shoe group.