I just finished putting 1 gallon of fuel through this engine at stock settings, and wanted to know should I start leaning it out at this time.


CAP

You should set the needles for optimum mixture when you flip the prop for the first time. Gassers should never be run with a rich mixture. You should mix a higher oil ratio but the only thing running the engine rich does is build up carbon.

Factory Presets are just that, presets. Just enough to get the engine running and let you correctly tune your engines carb to your temp, altitude and prop.
START ADJUSTING

I am spanking brand new to gas engines, stop flying for 7 months to run cars , but long story short , I see black spots on wing near muffler after flying could this be a sign of the mixture being to rich ? In the maual it states "after 5-10 tanks (2-3) hours) adjust the carburetor's L and H needles if necessary."

CAP

If the presets are to rich you could carbon up the rings, to lean and you could burn down the engine.
Adjust the carb so it is a tiny bit rich (100 RPM rich at WOT), as the engine breaks in you will need to readjust.
It ain't rocket science. Proper tuning will make YOU and your engine happier.
Black spots... too much oil, bad oil, too rich, engine is still breaking in...