I used the technique described in the Nitro Engine Tuning Guide book
Essentially it goes as follows after you have mounted installed etc....
1. Wrap head in several layers of foil
2. Get heat gun/hair dryer and get head up to 170 or so
3. Start her up. Let her warm up for 20 or so secs, then.
4 Then ease the trhottle up to wide open. Shoudl be very rich at this point puring out fuel. Use high speed needle to get the temp up to about 200 and no more. having a temp gun is important on the break in bench.
5 Run it at WOT (wide open thtottle) for 1 min then shut it down.
Repeat steps 1 - 5 another 5 times amkign sure to keep temp between 200 and 220
After 5 times increase run time to 2 min. constantly monitoring temp and makign sure it stays above 200. The propellor puts a fair airwash over engine and cools it so you may need a piece of cardboard handy to block airflow. I do this and it helps get temps up more quickly
after 6 x 2 min runs, repeat same process again but this time make it 3 min. Each time lettign engine cool down to at least 90 degrees before startign next heat cycle.
Do the three min drill another 8 times allways at WOT. During the last 3 times quickly pinch fuel line every so often. this causes the engine to rev up a fair bit more for an instant. keep temp between 210 and 230 all he time. use high speed needle to make sure this happens.
Once this is done you should have around 1.5 - 2 liters through the engine and can now lean it out for racing. If you have a tachometer its very helpfull as you can lean it out till you get max rpm and then back it off slightly with a 300 - 400 drop in RPM. You are now race tuned and ready to go.
People who have not done this will read this and freak out and tell you not to go WOT. Dont listen to them. The propellor puts enough load on the engine to keep it under 22000 rpm even at WOT so you are never in danger of over revving. This way you get temp up quickly in engine and actually reduce stress on conrod.
This method works. i have done it on 3 engines now and all still going strong with heaps of pinch after a season of racing.