Ignition for dummies (me)

[PStechPaul]

Probably anything from 0.1 to 0.5 uF, and 400V or more, will be fine. The capacitor (condenser) forms a tuned resonant circuit with the inductance of the coil primary and this provides a damped oscillation that can extend the time of the spark. A larger capacitor will give less voltage but longer time.

[PJW]

thanks for the info, I have found a capacitor locally  so I can have a go soon