Do you run it with out part of the fan cover/shroud off? I would not do that if so, it may seize from heat.
Have you done the green wire mod? They sell a blue cdi and orange coil that works really well for the ZXs, some people say it doesnt help but it does change the timing a little more than stock and the coil is higher voltage.
I dont remember if youre running pre mix or pump in, but if your running the pump in just add about an Oz of oil per gallon of gas in the tank and it will help raise the amount of oil ratio enough to be ok for it. You might have to run a larger jet when you do because it will help lean out the air fuel ratio by adding more oil into the equation and no extra gas actually less gas through the same orifice.
You will top out around 60- 65 with stock gears on it and that will be pushing it. Theres not a lot of options for after market gears for our scooters as you will find out. You can not use the dio secondary gears sold by the vendors on ebay, you have polini or malossi primary gear sets to choose from and thats it. I knew someone who had some secondary gear sets cut for him but not sure what the specs were. Either way its not cheap to change the gears, follow my link to see mine.
