Whew! We had a bunch of pips last night (six) plus one that pipped the day before and was a little bloody. This afternoon things have finally gotten moving in there. Three chicks are out: a bantam cochin cross who shot out of his egg like a rocket, and two EE, including the one that was bloody (seems to be OK). Of the remaining eggs, there are four pips. While there are still thirteen eggs that aren't doing anything at all, the clustering of pips and hatchings this time around is much better than it was last time.
Stitch81, that's a good question about how to tell how frequently the air volume exchanges. I can't think of a good way to test that, though. I think your idea of switching to a PC fan is a good one. The other thing you could do is to create a really good seal on the incubator lid, except for a few ventilation holes that you can control. That would make it easier to modify air exchange until you find the balance that works best.