If the high end NV adjustments are not having the effect they should have, I would guess you have crud trapped in the spraybar or a air leak somewhere. Maybe air leaking around the needle or in the fuel line or tank. Do you see bubbles in the line when running at full throttle? If not, remove the HS needle and backflush the spraybar with fuel.
I have a older saito .65 and it is a very smooth running engine that rarely ever dies in flight.