Welcome to the forums. The initial setting for the 125 is 1 1/2 turns out from lightly seated. Turn the idle speed up to about 1,700 RPMs. Slowly turn the pilot screw in until the engine stalls, then back it out one full turn. If it doesn't stall and no one has messed with the jets, sounds like your carb needs cleaned. Check for a hole in the float or a sticking float needle or debris between the float needle and needle seat.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.