Is this the style of carb you have on it?
May Racing Carburetor Air Filter 58MM For 2 Stroke Engine Motorized Bicycle 49cc 50cc 60cc 80cc (RED) in Air Filters.
www.amazon.ca
They only have an idle screw for adjustment. The only other way to adjust is a fist full of jets and then it's trial error to find the right one for your particular elevation.