I just had this same problem with one of my new bikes... It would only run with 1/2 choke!
I sealed up all the air leaks and checked everything I could think of, but had very little change.
Then I got the idea to drill the jet a little bigger.
I went to the LHWS and bought 6 tiny drill bits in the next sizes up.
Every time I drilled it a little bigger, I would test ride it & every time it rode a little better!
I stopped drilling when it was running good.
I thought I would add this to this thread incase anyone ever has this problem in the future.