Not sure about the Supercub - others will know though - but starting a Firefly on one mag has more to do with the fact that the left mag is equipped with a booster coil which emits a 'shower of sparks' to aid starting. The right mag does not have this device. Maybe the same with the PA18.
Checklists: BUMPFICH, FREDA and HASELL pretty much takes care of it all really.