So many different ideas on break-in. I even heard you use normal two stroke oil at first, because Synthetic is so slippery that it won't let the rings break in well. Then switch to synthetic.
Oyy vey.
it's ideal to use regular dino oil at first but not totally mandatory... the problem with most synthetics is that they are too slick and may not let the rings fully seat, I'm pretty sure this myth has been busted by now but on the other hand, it'll definitely break in better on dino or a special break in oil that some companies make for 2 smokers.
I like to run dino oil for the first tank then switch to the intended mixture for the rest of the life of the engines. Seating the rings is done by placing a heavy load on them by making lots of cylinder pressure... that means LOTS of full throttle acelerations then slow back down and do it again. Staying at any speed won't push out the rings as hard as a full throttle burst as cylinder pressure will always be highest under load at full throttle.
The most important thing to remember about breaking in an engine is to not let it overheat, and a fresh engine can overheat rather quickly since there's a lot of extra friction on the rings and cylinder wall so the easiest way to avoid overheating is to keep your trips short, no more than 10 minutes for the first run, then go up to 15 minutes for the next several runs. It's best to let the engine cool all the way down between runs also since running it for 15 minutes, then giving it a 10 minute break won't let the engine cool very much, then on the next 15 minute run it'll be at or above operating temp by the time it has run for around 5 minutes. These engines cool down pretty fast and 30 minutes is enough time to let one cool, it also helps to place a fan blowing at the engine but not totally necessary as using a fan to cool it down may bring the time from 30 minutes down to 25 etc...
Once you've got about 5 or 6 15 minute runs in it's safe to bring the run times up to 30 minutes or more if you wish, by this time the rings are still far from seated but you should notice the engine loosening up a little. By the time you're done with the first tank of fuel you can run it as long as you wish but keep an eye on the temperature. I use an infrared "point and shoot" thermometer to watch mine by parking the bike and taking a quick reading. These can safely run at temps as high as 360F but some people like to keep them under 300F. at somewhere around 400F is where damage starts to happen like scuffing the inner cylinder walls or even seizing a piston.
Part of the overheat prevention is done for you at the factory because they set up these carbs really rich and this helps keep things nice and cool, a Fred head or a Puch head, or any large billet or cast head will also keep the temps in check really well. Mine stayed at around 320F during break in with a Fred head installed. There are a few billet heads that won't help the cooling that much like the ashtray head, the RSE head, and I've seen another smallish square shaped billet head with really thick fins that wouldn't be able to keep a fresh engine cool enough for a long run on a fresh engine. The stock heads are the worst hands down for keeping things cool so keep trips short as I mentioned earlier if breaking one in with a stock head... Also, this is NOT the time to tune the carb if you got a stock or one of the small billet heads... let it break in first then you can lean it out afterwards, these heads will get up to 360+ rather quickly as it is.
It's ok to swap carbs on a fresh engine too, just set it up a few jet sizes richer.
The whole break in procedure is really doing only 2 things... loading up the engine to seat the rings, and keeping the trips short to prevent overheating... Just about everyone's procedure covers these 2 parts in their procedure and the rest of the break in can be done however you choose, the main idea is to not let it get too hot in this time because of the extra friction until the rings match up to the cylinder better and better.
