No idea what a starting point would be for a 125, but it'd be expected to be a bit richer than a 250/300 for sure. The best way is to provide as much info as you can. Current settings (carb size, pilot, main, needle and clip pos, slide number) and conditions (altitude, temps, fuels, oil ratio, etc) and then.. how the bike runs now, and how you'd like it to run. The more info you supply the more likely people will be able to chime in with suggestions.