I had the same problem i fixed it last week
If u have those symptoms:
Smell when u fill up the tank
Smell when u do hardturns
smell when u drive fast and use kickdowns
then u have my problem: as JPM said, its the fuel pump. If u feel like DIY, then just take off the seat, unscrew the plastic-metal like cover and then u can see the pump. If its already swimming in gas it is the problem. try to unscrew the circle cover and see if the rubber pad that seals the big circle like thingy is not loose (this was my problem)
U might as well try Furious's cardboards thingy, but u have to be kickin on the pedal for some time
Good luck !