The nice thing about the AX series of OS engines is that they will fly just fine even without a specific break-in period. And, as mentioned, they are a tad bit rich on the low end out of the box, but that's ok. That can be tuned out after the engine has burned some fuel.

I have three 1.20 AX's, and a pair of 75 AX's. I did the traditional thing with breaking in the 1.20's, sat it on the ground for at least two full tanks, run rich, then lean, then rich... and so on. Then flew them. Flew just fine.

I then bought a .75 and put it on the Protege. Well, I did the traditional thing with the first tank, and found that it ran just fine no matter what I did... so I flew it after one tank, and it ran fine. Plenty of power and very smooth and quiet.

Next, was the .75 on the Skylark. Well, no break-in, just filled the tank, tuned it, made it a tad rich, then put it in the air. I tended to fly it easy for a few orbits, then hit it hard for a few orbits, then eased up a bit.. continued that.

I had it up today for the 5th through 9th flights (all full tanks) and there was absolutely no indication of anything that I could even suggest as being problematic.

These engines are fantastic. So, if you are concerned about the manual and the instructions, get an OS AX series engine.. then you professor will not hesitate to give you an "A".. or at least an E for Effort... or maybe "E"XCELLENT CHOICE!!

CGr