Steve -

Are you suggesting that the high cylinder pressure due to combustion might:
 
A)  Cause the spark not to form, since the air won't break down and ionize?

B)  Or instead are you suggesting that the magneto will not try to make a spark?

I'm no expert, but I think (A) would be unlikely, and (B) doesn't seem feasible since the magneto has no way of knowing what the cylinder pressure is.

The operative phrase here is "I'm no expert".

- Rob Wolf