A friend of mine had this same problem with a new engine last year. The engine would start and run ok up to about half throttle. Anything above half the engine would die. The problem was that the low end needle was too lean.
We finally figured out what the prob was when I was able to turn the high end needle almost completely out and it still run ok. The lack of smoke was also a huge indicator. Should have been super rich and blowing lots of oil but it wasnt.
After richening the low end a 1/4 turn at a time we finally got the high end needle to respond. From there we then fine tuned the low end an 1/8 turn at a time.

Good luck,
James