Why does my car smell of petrol intermittently?

it could also be to do with your exhaust

i run a decatted exhaust system on my car, and it can smell very rich of petrol sometimes, but other times its not noticeable

my project car also used to smell of petrol when it was running, but it was constant (rather than intermittent) and it turned out to be a leaky fuel pump and the timing was out by a couple of degrees

this would make me advise you to check your exhaust system :)

Obviously there is a leak somewhere. Since petrol evaporates rapidly it would be difficult to locate the leak. Since you notice the smell when accelerating I'd suspect it to be toward the rear of the tank and toward or on the upper side: Possibly the evaporative emission hose has become disconnected from the tank.

Get on a private lane (or some place where there is little or no traffic) and see if you can force the smell to appear by accelerating hard. Then come to a gentle stop, shut off the car, get out and smell beneath it from front to rear on both sides. Also smell in the engine compartment. That may help you or the garage pinpoint the area of the leakage.

I would have the fuel system pressurized with a smoke machine to see where vapor is leaking from. It's most likely an o-ring seal that is leaking and causing vapor to build up in the underbody chassis or wheelwells, or most likely under the hood. Take it to a mechanic immediately.

because something isnt working properly