Abstract: A programmed timing control controls the occurrence of timing signals relative to engine position in systematic relation to engine speed to provide such spark at a time appropriate for a first fuel at each engine speed. An alternative fuel timing control produces a controlled timing interval systematically related to engine speed and changes the timing of such spark by the controlled timing interval to provide such spark at a time appropriate for a second fuel at each respective engine speed. A variable dwell control provides a dwell control signal for controlling the application of current to the ignition coil. A signal generator coupled to the timing means generates a time varying signal rising in magnitude substantially monotonically and preferrably lineraly with time following each interruption of such current until a later time corresponding to the next succeeding interruption of such current.