It's got to be a fuel leak, there's no way it could run rich enough for you to smell it.
If it was that, where would the smell come from? - the exhausts so you wouldn't smell it in the car.
It has to be blowing off the engine into the cabin.
Check the hoses for leaks by going out early and putting talc around the fuel hose joins. Then when you start it up you can see where the fuel has leaked.
The leaks on mine were under the regulator (tightening didn't fix, I had to take it off and replace the hose) and the worst one was under the throttle pulleys at the front of the engine joining the fuel rails. There are a couple of other pipes under there too.
To fix the one at the front I had to take the throttle bodies off which was a pain in the arse. If it's the others it would probably need the plenum to come off :(