Dave:
I assume when you say "gas" you mean fuel and not exhaust. If that is the case you most likely have a fuel leak somewhere. Check the carburetors first - check all fuel hose connections and make sure they are not cracked and that the clamps are tight. Also check the plugs at the bottom of the float chambers, there is an O-ring seal in there that deteriorates over time and allows fuel to drip out. If all of that is on order then check the fuel pump and the associated connections to the pump for leaks.
Most likely you will find the problem at the carburetors or fuel pump. If not you need to get under the car and inspect the fuel feed and return lines from the tank, pump and carburetors for cracks or breaks. It is unlikely that the problem lies there, however.