Modeling Capacitive Discharge Ignition (CDI) Circuit
Modelling the spark gap is the "fun" bit. I'd recommend downloading a student edition of microcap and using their sparkgap model: -



As for the transformer, this is modelled as two inductors with a coupling coefficient (k in microcap and m in spice I believe). The coupling coefficient dictates the amount of primary and secondary leakage inductance. You'll also need to model exteranl resistors that represent the winding losses and quite probably a few hundred pF across the secondary winding.

Here's the spectrum (suppliers of microcap) explanation of the spark gap. Maybe you can make use of this article in other simulators?