First thing to check is the part you throw away! 

What does the resin flow look like:

less?
more bubbly?
frothy (moisture!)?
even and symmetrical on all 4 sides?
glassy (good vacuum)?

If flow has not changed then process parameters might be OK although a 10%
increase in P2 or main laminating pressure should cure a "borderline" void
problem.

Tip:   Make a design on paper of crosses 1 inch apart.   Photocopy this and
locate under the first ply of pre preg (use several sheets to get coverage).
The ink in photocopies is just perfect for seeing how the resin is flowing and
identifying low pressure areas (which can be responsible for voids).

George Wheadon, Nelco Europe