Hello pat31, the 1/8" root opening sounds a bit tight, 1/4" is a more traditional specification on the root opening for that plate thickness/bevel angle configuration and process type. I can see 2 issues that could be a factor for having a tough time with the particular set-up that you're describing, you'll have a hard time keeping your stick-out short enough without having to go to a special tip/nozzle combination(many guns will have a nozzle that has an internal diameter of 3/4", next offering is typically 5/8", then there is one that is even smaller but it requires using a special contact tip along with the special nozzle). Due to the 1/8" root opening it is real common for the root bead to bridge over the backing bar, tie into the two edges of the plate and not tie into the backing bar, in the process a large amount of slag can be trapped underneath. Using a standard nozzle with the bevel/root configuration that you have described will force you to run such a long stick-out for the root that you will possibly see a lot of wander in the wire position due to the cast that is in the wire and the long distance that is being held from the contact tip to the weld pool, you may also notice that the burn that you normally see on the end of the wire isn't as consistent as it is when you are welding with the 1/2" to 5/8" stick-out that you usually would run. If you then have to run this same plate set-up in the overhead position it can be even worse.
     If allowed I would increase the root gap to 1/4" and use a 5/8" diameter nozzle, I believe you will be pleasantly surprised with the ease with which this combination will make for welding the root in. A few thoughts for consideration, good luck and regards, aevald