the secondary ignition coil 10 b and the spark plug gap 12 a significant feature of the circuit 100 is a resistor that allows an ignition control unit 180 to vary the duration of the spark event more specifically ignition coil 10 is connected to a blocking capacitor 120 which prevents the low frequency discharge of a follow on capacitor 130 from flowing into the secondary coil 10 b the follow on capacitor 130 is charged from a voltage source 140 through a resistor 150 voltage source 140 can be a variable voltage source resistor 150 defines the charge time of the capacitor 130 and limits the spark duration capacitor 130 discharges to node a which is interposed between coil 10 and the spark gap 12 discharge is through an inductor 160 and a resistor 170 inductor 160 helps limit the peak current whereas resistor 170 acts primarily to set the time constant of the circuit 100 in the example of fig1 resistor 170 is a variable resistor fig2 and 3 compare the spark duration of a conventional coil ignition circuit fig2 to that of a coil ignition circuit having an extended duration follow on current circuit such as circuit 100 in accordance with the invention fig3 specifically fig2 and 3 show the effect of adding the follow on circuit 100 to the stock coil 10 circuit.