Is the engine broken in yet? If you're still in the first couple of tanks, it probably isn't. Poor transition from idle to high throttle is a common problem on new engines. The low end needle setting will usually be the peoblem after break in. Once you have your low end needle properly set, you shouldn't have to fool with it again unless you make a large change in fuel nitro content.

Set your high end needle to max rpm, back the engine down to a fast idle. Let it sit there for 15-30 seconds and then advance the throttle quickly. If it doesn't advance smoothly, adjust your low end needle in or out about 1/4 turn at a time until the engine will sit at a fast idle for a period of time and still advance relatively smoothly. Perform all your low end idle adjustments with the engine at a fast idle.

When you have the low end set, you will probably have to adjust the high end again slightly to get max rpm less about 200-300 rpm. Use a tach if you can. All this after the engine has 4 of 5 tanks of fuel through it.