I inject moulds of a similar size to the one that is giving you
trouble. Here are a couple of things that I have learned.
Wax too hot is as much trouble as wax too cool. The very fluid wax
appears to not have enough density to push the air out into the
vents. Try starting with a cold injector and inject the molds as it
warms up. This will give you are variety of samples of temperature
and you might find one that is better. Although not always a good
idea, you can try using a dusting of talcum powder for these molds.
Work the talc into the vents. Blow away any excess. The talc will
hold the vents open a little and allow air to pass through them
If the mold is cold the wax will cool too quickly on the surface of
the rubber and not fill completely. Try warming the mold a little.
I do this by setting a cloth on top of the wax injector and then the
mold on top of it. Do not let it get hot, that is harmful to the
rubber. Do get it noticeably warmer than room temperature.
Increase the air pressure that you use for this mold. I will often
use about 12 lb of pressure.
Different waxes of course will behave differently and you way want
to try a wax for filigree type of models.
I have overcome the problem that you are experiencing by using all
of the above and am happily using my 25 year old injector.