Firstly, you must always adjust the mixture screws on a new gasser. They are not "factory set" but rather set to a known position so that you have a starting point by which to begin adjusting.

The low needle on a gas engine affects the carb mixture from idle to full open throttle. The high needle affects the carb mixture from a little past half throttle to full throttle.

Set the low needle first for good idle and responsive transition to about one third throttle when you work the throttle from idle to mid rapidly. Once you have the low needle set for a reasonable transition then adjust the high needle to max rpm with a tach, and back the needle open a little to make sure the mixture is slightly rich by observing the rpm decrease by approximately 100 rpm from peak.

Now to set your idle after the carb has been adjusted properly, use your ATV's(automatic travel volume) on your transmitter to adjust the low end of your servo travel to your targeted rpm range. Make sure that you do this with your throttle trim at mid-range setting.

If the rpms slows down on vertical lines whilst flying, open up (CCW) the high needle about 1/8th turn and fly again.