This topic has been hashed over, and over again, but here goes:

Follow the instructions. If they are lost, lots of 5 min runs, with 10-20min cool down in between. 1st run, 3 turns out, full throttle for 1 min with glow plug attached. Slowly tune for that point where it goes between 4 stroking and two stroking. Next runs, lean it a click or 2, pinch the fuel line for a split second, it should jump in rpm, if it dosen't it's too lean, back it off. Pinch it every 30 sec, just for a split sec. Eventually it'll make less and less of a difference. More 5min runs like the last, all at full throttle. You should see plenty of smoke out of the muffler, NEVER lean it all the way for max rpm. When you have 30 or 40 min total run time, try to set the idle. If it will not idle, a few more 5 min runs should help.

Fuel should be low nitro with 20 plus percent oil. Lots of castor in the mix. Never run it slobbering rich. The metal will not come up to operating temp this way, the sleeve will not expand all the way, the sleeve will wear in at the cooler temp, and when you do exentually run at a leaned out 2 stroke hot setting, it'll never produce the power it was capable of. GMS are very good, powerful engines, and require longer than usual break-in.

After it's had 30 or 40 mins worth of 5 min runs, I usually go fly, (rich). Do lots of loops (not all in a row of course), at different throttle settings. This way it leans a bit, then richens up. Lean it up just a bit between flights. It'll really last a long time if you keep it off peak. I point the nose straight up, and tune so a quick pinch will audibly bump the rpm.


Here's some more threads:
http://www.rcuniverse.com/showthread...kin#post348166
http://www.jettengineering.com/faq.html#faq8
http://www.rcuniverse.com/showthread...kin#post431044
http://www.rcuniverse.com/showthread...ch+and+breakin]