So you went from 78 pilot to 120? Or you went from 78 mains to 120? (sorry, just want to verify)
Have you pulled the air screws and made sure there is an o-ring (in good condition) around it. I had a bike that was driving me nuts, then I pulled the air screw and found a washer in there....missing the O-rings under them. Ran much better after that!
One more thing, did you open your fuel tank filler lid to see if it was venting well enough?
As for the float, when upside down you are putting pressure on the little spring in the bottom of the float needle. If one droops because the spring is being loaded, and the other doesn't droop because the spring isn't working, that could be a problem too.