Engine speed responsive means for changing the position of a vacuum spark advance limiter stop

Claim 1

In a vacuum spark advance mechanism for an internal combustion engine of the kind in which an operating element of an intake suction operated spark advance motor is connected to an electrical interrupter mechanism controlling some of the timing of the ignition advance or retard and is normally movable to a maximum vacuum spark advance position by high engine intake suction from the engine when transmitted past control valves, the improvement comprising, limiting means for limiting the movement of the operating element to an amount less than said normal maximum vacuum spark advance position while still permitting a substantial vacuum controlled spark advance, speed responsive means associated with the limiting means for changing the limit on the movement in response to a selected change in engine or vehicle speed to permit a greater amount of movement above the selected speed then below the selected speed, said limiting means including a mechanical stop element having first and second stop surfaces for engaging the operating element to limit movement of the operating element, and positioning means associated with the speed responsive means and effective at speeds below said selected speed to locate the first stop surface in an operating position where the first stop surface can engage the operating element and effective at speeds above said selected speed to move the first stop surface from said operating position and to locate the second stop surface in said operating position.