[wheelbender6]

Jetting up from factory jets is always a good idea. It helps power and even engine longevity.
-First, drop the float bowl and determine your existing main jet size and type (the Keihin style jets look a little different from Mikuni style jets). GY6 usually has Mikuni style. Plenty of comparison pics on the internet.
-Order the next three larger sized jets from your factory jet. Sometimes you can get a jet kit with 3 different sized jets in it.
-Try the different jets. Warm up the bike and do a top speed run for a few miles. The correct jet will cause your spark plug insulator to look tan, or egg shell color when you remove it.
-If the insulator is white or very light tan, you need a bigger jet. If the insulator is dark gray or black, you need a smaller jet.
-This is hot rod tuning 101, and applies to any carburated piston engine: Scooter, car, airplane, boat, etc.