If nitro engines were as sensitive to the exact conditions of break-in as many people think, they never would've been a practical power source for toy cars anyway.
For the first tank or two, run it so rich it can barely rev-up and move the vehicle, then gradually (i.e. over the next several tanks of fuel) start tuning for a peak operating temperature around 230-240F. It will still be somewhat rich at this point, and it won't run very fast, but leave it alone until it starts to have trouble warming up -- at that point you know the piston has fully-seated in the cylinder sleeve's pinch zone, and it's no longer generating excess heat from friction. Then you can start tuning for maximum performance.
The really nitty-gritty details are just like waving a Polaroid photo to make the image appear faster -- it doesn't really make any difference, people just enjoy believing it does.
EDIT: Oh, and don't be afraid to turn the fuel mixture needles less than 1/8 of a turn as necessary. That's just a rough guideline. Every engine I own has a sweet-spot that I could only reach by tweaking the needles by barely-perceptible amounts, 1/16-turn or less. And give the engine a couple minutes to respond to any changes you make, because it will take that long for the engine-block temperature to increase or decrease by a meaningful amount. Don't go making changes ten seconds apart, that's how you end up over-leaning the engine and burning it out. (I learned this the hard way -- I broke-in a new engine the way I described above, then I got impatient and started tuning it for maximum performance over the course of about 5 minutes. When I saw the temperature I wanted, I decided to go have fun, and ten minutes later the engine's temperature was 413F. Amazingly it was still running, but needless to say, it never ran properly again.)
Last edited by fyrstormer; 01-07-2015 at 02:17 PM.