Congrats. You've already made it farther than the dude going to Africa in the modded jeep!
You are running rich, too much fuel - that is the cause of the black smoke. I'll bet if you pull a plug now it would be sooted up pretty good. My first thoughts are to:
- make sure the choke butterfly is in the position you think it is (I'm sure it is, but it's the obvious)
- reduce fuel flow with the main fuel jet needle by leaning it out some, usually that is screwing the needle in some
- verify that the throttle linkage is in fact moving the throttle butterfly
The valve train was dry and took a bit to move oil up there and quiet it down. If it's been inoperative a while I'm sure it just needed to get primed again - if it persists check that there is no sludge blocking the oil pump. Remember to keep an eye on the oil pressure gauge, if it's too low we need to diagnose that before we have to open up the bottom end.
Have I mentioned how much 6 volt systems suck? When you get this tuned you will much prefer the hand crank.
ETA - on the throttle linkage. There is a governor involved there somewhere - so when you get it running again reach over with your hand and push the throttle butterfly to see if it changes the engine RPMs. If it does and responds like it should then we need to check and make sure the governor linkage is set and there aren't any stuck linkages somewhere. Also, it can be wonky because of old or dirty oil and wake itself up just like the drive train. Stating the obvious the governor limited the throttle response with a set of spinning counterweights that helped the engine maintain RPMs under load and then kept it from 'running away' when the implement was lifted.