How to break in an ABC type engine causes more controversy and arguments than just about any other subject and about the only thing that's agreed on is to use more oil (especially some castor) and never to run it too lean.

My personal preference is to set the mixture quite rich to the point where the engine is just breaking between a 4 stroke and 2 stroke sound. This is basically what nearly all manuals recommend depending on how you want to interpret them. Rossi calls it "greasy exhaust" for instance but any setting that's very rich but not quite into a 4 stroke is fine too. Run it at this rich setting for about 20 minutes (a couple of tanks) then start leaning it out slowly over the next one or two tanks and it should be ready to have the idle mix set and go flying. Avoid leaning out to peak revs though, keep it at least 500 below peak revs.

Now the arguments will start