[TheForge] Modified Side-Arm Burner Troubles

[DillonCo]

I'm having trouble with my modified side arm burner
(http://www.geocities.com/zoellerforge/sidearm.html).  Although it works
well outside the forge chamber, when I light it inside, the flame quickly
destabelizes (at any pressure).  The flame disappears and very light (cannot
be see in daylight) blue wisps come out of the exhaust (at are visible in
the chamber).  I believe the problem is insufficient oxygen because I cannot
light a match in the chamber after turning off the propane.
Can anyone help?
BTW, it's not built perfectly.  I used a symmetric T and a bushing instead
of an a-symmetric T, and the plug wasn't drilled quite straight (at propane
nipple is about 2.5* of level).