As a general rule how should I use my tachometer to setup the carburator needle, I mean from the peak rpm how far should I go back(500, 1000 rpm).

Back off about 300-500 rpm.

Does this deppend if I'm usimg a 2 strokes, 4 strokes or gas engine.

I've never used gas so I couldn't say for sure, otherwise 2 or 4 stroke glow would be the same.

Thank's man