All Plugs Fouling on Right Bank

Hmm i guess it could still be rich and have a stumble as well.
Get a buddy to stand behind your car. let the clutch out in first gear, so it's just idling down the road. them punch it!
IF Black comes out the tail pipe, you're probably still rich.
Now you said "The engine runs best when the idle adjust screws are full open (rich)." This tells me your two LEAN.
I agree with AJ, if there is holes drill in the butterflys, this could cause your problem as well!!!!