Adjust your high speed needle for maximum RPM. Do this slowly, just a click or two at a time until you get it right on. Then back it out (richen it) 2-3 clicks or until it loses 200-300 RPM. Next, set your low speed needle. If it is lean, the engine will usually die when you advance the throttle. Usually these come little rich from the factory though and it will sort of sputter and hesitate as you accelerate. Slowly close the low speed needle 1/8 a turn at a time until you get a reliable idle and smooth transition.

Once you get the .55-AX set right it is very, very reliable. I have noticed that the high speed needle isn't quite as sensitive as some engines. Be sure to use a tachometer. I have pretty good ears and I can use them to tune an engine fairly good but they are still not as accurate as a tach.