Your best bet would be to get a jet kit instead paying per jet prices . Here is a jet kit
http://www.partsforscooters.com/114-...ategory=133078
Most have the fuel/air screw covered up and no clip to adjust the needle position so a carb you cab tune would be a great buy . Here is 4 diff types that come on the Gy6 50
http://www.partsforscooters.com/Stre...tors-and-Parts
The airbox does not choke the airflow so a cone airfilter with a stock head and exhaust will surely make it leaner and not perform well like it would on a BBK , ported head or unrestricted exhaust . Remove the sparkplug and compare the color of the tip to this chart
http://www.4secondsflat.com/plug_chart.html If you get the jet kit or other jets once you think you have it dialed in install a new sparkplug , run it down your strett hitting the top RPM and hit the kill switch . Remove the plug and compare it to the chart above .