Run the engine on the ground for 1-2 thanks of fuel. Adjust the high speed and low speed needles as per the instructions. Don't adjust the regulator until the engine has a little time on it. The regulator will be very close to ideal when the engine was shipped and should be just fine until you get it broken in. After the initial 1-2 tanks on the ground, just go fly it, keeping it just slightly running rich. As you get more flights on it and it gets more reliable, keep fine tuning the high and low speed needles. Adjust the regulator only if it is needed. The regulator will seem to have the most effect in the mid rpm range. Here is a good article on tuning the YS engines.
http://www.geistware.com/rcmodeling/...ys_engines.htm
Paul