Check out riverol's post:
"It was difficult to find that small amount of gas because it evaporated as soon as the engine warmed up."

http://www.brickboard.com/RWD/index.htm?id=596675&show_all=1
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Tom F

On my 1990 760, there was fuel vent hose that goes over the rear axle that had a crack in it. Sometimes it smelled like gas and sometimes it leaked gas if I filled up on an incline.

It is only a suggestion, my 89 740 had a strong smell of gas and it was the fuel pressure regulator dripping gas from a crack in the vacuum line. If that is not the problem, I would have the fuel pressure checked before the main fuel pump, after the main fuel pump, and from the fuel pressure reg. to the tank. You shoul find a pressure drop between those areas faster than normal, if you do, then just narrow it down from that. ie. injectors, fuel lines, bango connectors and lines to the fuel tank. The gas smell is hard to really pinpoint by just the smell, because the smell lingers everywhere.

Check your gas cap. Sometimes if they are not screwed on properly you have the problem you described.