Most people will say just read the manual and do what it says...but have you ever tried deciphering something like the Rossi instructions?? Both Rossi and Jett (who you gotta admit make some pretty good engines) say that you have to run them in for between 30 and 40 minutes at what they call a rich setting. The problem is that this "rich" setting isn't particularly well defined (Rossi for instance says the exhaust should be "greasy" ) but by reading between the lines it seems that what they intend is for it to be running in a 2 stroke but that even one or two clicks richer will make it drop back to a 4 stroke. In other words, run it at a point just beyond the transition from a 4 stroke into a 2 stroke mode.

The official OS engine web site (not the American importer's but the factory) actually says that the first run should be one minute in a rich, slow 4 cycle then the remainder of the first tank should be cycled every 10 seconds between a 2 stroke and back to the rich 4 stroke. Then 3 or 4 tanks with the needle set so it's just broken into a 2 stroke.

With all of this I've tried to avoid just giving my own opinion. But one thing that Jett states is that the majority of the running in is not for the ABC piston/liner but for the con rod.