As a lot of people will tell you, there is no rule for that, and the factory settings would be just a startng point. Every engine needs to be adjusted according to the operating situation, propeller size, altitude, etc.; however, a good staring point would be 1 3/4 turns open on both needles, and once you have it operating, you could start adjusting. Remember to stop the engine to adjust the needles, and also, once you adjust the high needle, go back to the idle, and double check it. Once you have run the engine rich for a while, you can start leaning it to get better performance and stability, but don't lean it too much during the breakng in period, and you will get better performance and durability overall.

Kind regards.