I have several OS AX engines. All of them, ALL OF THEM, ran just fine blubbery rich for the first two tank-fulls. I would run them up to full at a somewhat lean setting so I could get it there, and got it there with no problem, by the way, then richen it up so that it sounds like a four stroke and pumped out the blue smoke like crazy.. spitting oil and fuel, but still runs.

I would run it full at that blubbery setting, for a full minute then lean it out a bit to allow it to get up in RPMs for about 20 seconds, then back to blubbery rich again. I would repeat this for the full first tank, then refuel, and repeat, but a tad leaner on the blubbery side and increase the leaned out time to about 30 seconds.

After the second tank was finished, I just fly the thing, and run the engine a few clicks rich. Yeah, I get lower RPM's but it will run cooler and break in just fine.

The more you fly that engine, the stronger it gets.

CGr.