Flame kernel generation is essential to the stability and efficiency of combustion in a spark engine. In this study, the initial process of flame kernel generation was studied in an optical spark engine. The engine was operated with the λ adjusted from 1.0 to 1.5, respectively. Meanwhile, the continuous arc motion was inventively quantified. First, the impact of single-coil and multi-coil discharge on the stability of the combustion and knocking tendency are examined. Secondly, the differences in arc development between single-coil and multi-coil discharge and the effect of the shortening phenomenon on the generation of the flame kernels are compared by optical images. Finally, arc shortening feathers (including timing, extent, and spatial location) are statistically analyzed over multiple cycles in conjunction with combustion phase. The results show that multi-coil discharge can make the flame kernels larger, which could keep the flame kernels from quenching. They also show that variations in arc shortening are linked to cycle-to-cycle fluctuations. Furthermore, a principal component analysis is done on the features of the first two arc shortenings and the CA05 phases. Precision control of the arc shortening features can greatly enhance the spark engine’s initial flame kernel stability and lower cycle-to-cycle fluctuations.