First if your fat go to the gym, second buy it a performance kit, third go to www.partsforscooters.com they have a wide variety of performance parts for scooters, dirtbikes, and minichoppers at low prices. it is a good website to order from i recommend it.
if you are talking about a full size scooter you would have to get a CDI that has no rev limiter and remove restrictions in the variator and exhaust.
that is how you do it cheaply, of course there are mods available to improve performance.
but a engine in it
the brake
An improved flow of air and fuel mix will make the scooter faster. You can do this with an aftermarket exhaust.
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Go downhill
Loosen the headset a bit.
Yes it will make the scooter go faster, but you could run the chance of blowing parts in the moter if you do so
Really nothing get a 150cc
lose some weight
push it off a cliff
get a gas powered one
Unlock the gas on the handlebars