yeah 2 turns out is standard, but if youve done anything to your scooter that affects the mixture (changing air filter or jets), you should perhaps turn it more in or out...
With the modifications are this: if youve changed filter to one, which lets more air come in, you should turn the screw tighter(clockwise), and if youve up-jetted, you should turn it looser(counterclockwise).
Be aware that you will rarely or never have to turn it full 3,5 or 4 times out... if you do this, and it still runs poorly, change the bigger things (jets, air filter and stuff), as the mixture screw is only for fine-tuning