clutch is disengaged or a gear position is neutral and whether or not the throttle is closed on the basis of the engine speed ne throttle angle u03b8th and rate of change u03b4n in engine speed when the engine is in the no load deceleration state a switching unit 106 is controlled to connect the advanced ignition timing setting unit 102 to a converter 105 when the engine is not in the no load deceleration state the switching unit 106 is controlled to connect the standard ignition timing setting unit 101 to the converter 105 the converter 105 determines an ignition angle u03b8 ig on the basis of output pulses of the pulse generator 24 and the advance amount or retard amount provided by the standard ignition timing setting unit 101 or the advanced ignition timing setting unit 102 the arc energy supplied to the ignition coil 25 is interrupted at the ignition angle u03b8 ig thereby allowing the ignition plug 26 to ignite at an optimum timing with reference to the flowchart of fig2 and the timing chart of fig3 operations of the ignition control unit 10 will be described the flowchart of fig2 focuses on the processes in the no load deceleration state determining unit 104 in step s 10 it is determined based upon an.