Gas leaking out exhaust manifold?

I hope you guys can help us out. My brother in law has an 83 Buick Lesabre with a 307. He claims iIt appears that gasoline is somehow leaking out the exhaust manifold and it has been terrible on gas mileage since he bought it a couple of weeks ago. He's also smelled gas coming from the engine compartment at times. It seems to be running okay other than this leaking gas and it only seems to leak when he first starts the engine? Hope someone can help.

The gasket on the Carburator might be bad. That is my best guess