petrol smell while driving

[Larry]

Just bought a 2004 Peugeot with 315k on the clock and while driving down the highway doing an average speed of 100kmh I started smelling a faint but obvious petrol odor coming in through the window. The window was open but the smell faded after closing it again. I have had this car for less than two weeks and taking it on Friday to get the timing belt done. It has not been changed for over 150000km. - Otherwise the car seems to be in quite good condition but that new petrol smell is strange. Any advice where to start looking or diagnosing? - Im new to French cars.