Firstly I question why you have those injectors. Stage 1 defines an increase in boost pressure, along with a suitable calibration (i.e. EPROM) for the same.

This makes me believe it may be more than stage 1?

This aside, misfires are a common issue, chiefly due to the antiquated ignition system.

When boost pressure is increased, as is cylinder pressure which is what results in the phenonium of the spark being "blown out".

What are your plugs gapped to?

Martin