renault espace 1993 petrol smell only with the windows down

[matthieus5s]

Hi, can anyone help me with my 1993 renault espace petrol 2 litre.
I get a strong petrol smell in the car whilst driving uphill normally, but only when the windows or sunroofs are open! I have looked all over for a leak but have found non. Ive checked out the tank by lowering it down & have blown through all the vent pipes. I am very good with cars normally but this is baffaling the hell out of me.