Hey Jason;
Their are varied opinions on "how to break in a new engine"...lol. I'll give ya the most common method, and the one I always use...
The needles should be set from the factory (depending on the manufacturer), but basically you want to get it started running rich, and idle it around till the tank of fuel is gone, giving it just enough throttle to keep it running. When it stops running, make sure you turn the flywheel so the piston is at BDC (bottom dead center, at the bottom of the sleeve) while it cools down. Wait til it's completely cooled down, turn the high speed needle in about an 1/8th of a turn, and repeat the process. Do this for about 5 tanks of fuel, making sure that the engine doesn't get too much over 200 degrees for the first 3 tanks, then making sure that it doesn't get much over 225 for the last 2 tanks of fuel.
Beginning with the second tank, you can give it longer bursts of more throttle, kinda starting with 1/4 throttle with the second tank, then 1/2 with the 3rd, etc...
The break-in process is the same for a new piston and sleeve, as it is with a brand new engine. You might want to replace the rod too, as they sometimes fail after putting a new piston and sleeve, cuz they aren't designed for the stress of 2 break-in processes...
Hope this helps...Let me know if you have anymore questions....TTYL..
Brad