Again, check the manual, if you've got one. I see a lot of comments about ~150W bulbs for many popular enlargers, so it could be your 85W bulb is too dim. (My own enlarger takes three 35W bulbs, but it's a weird one.)The lens is new and free of fungus as is the bulb (new) which is an 85W halogen type.
That might help -- but as you say, you've got rather long exposure times to start with, so unless/until you improve the brightness out of the enlarger, stopping down may be an awkward solution.In terms of vignetting, does it happen with wide open apertures? Would I avoid this problem stepping down a few f stops?
I'd expect that would depend on whether the problem is primarily with the diffusion (or condenser) light source or with the lens. You could certainly try it; that might be a useful diagnostic test. Be aware that you'll need to raise the head higher to get an equivalent-sized print when you switch to a longer lens. Since you're talking about an 11x14 print, this will mean a pretty high head height -- perhaps higher than the enlarger supports. Most enlargers let you tilt the head for wall projection or reverse the head to project on the floor for situations like this.I have a 105mm that I use for my 6x6 enlargement. Would using this lens change things?
There are so many variables from my own equipment and materials that I can't give you a definitive answer. Certainly I wouldn't get many 30-second exposures at f/2.8 to make an 11x14 with my equipment and materials. 30 seconds at f/5.6, perhaps, but not at f/2.8.Paper used Ilford MG FB glossy. Does 30 seconds sound too long for an adequate exposure for a 11x14 enlargement at 2.8?