Originally Posted by Dredd
This sounds like it's lean. At the top end the engine is starving for fuel. I'd open up the high end needle 1/4 to 1/2 of a turn and run it again. See what happens there.
I agree with Dredd, sounds lean. Sounds like the LS needle is set ok which gives you the nice stream of smoke up until the HS needle kicks in. The engine can also bog if the HS needle is too rich.. Try turning the HS needle anticlockwise 1/4 of a turn at a time(remember where the original setting is). If you dont get a result after doing this 3-4 times go back to the original setting you had and try leaning the HS turning it clockwise.
Hope this helps, good luck...............