Looking at the generator from the brush holder end, (opposite the pulley) the Armature terminal is the one nearest the top of the housing. The Field terminal is further down the housing toward the bottom. Look into the back end, and you'll be able to see that the field wire is much smaller than the one that takes the charging current from the armature.
If the spark plugs and tailpipe are sooty, that's from a too-rich mixture. The carburetor could be flooding for some reason, or the soot could just be the result of lots of idling and no on-the-road running. Unless you're seeing black smoke out of the tailpipe, at least some of the sooty deposits should clear up once the engine gets a few road miles on it.
If the generator has a lot of black deposits near the brushes, that's normal brush wear. They're made of carbon.
Jerry
Edit: In this pic from the tech tips article, the Armature terminal is at the 9:00 position, with the Field terminal below it. The wire from the insulated brush is always attached to the armature terminal. The field coil lead is the tiny wire that's not attached directly to the brushes.
http://www.stovebolt.com/techtips/6v_charge_system/6volt_e.jpgJerry
