One thing that many of us have forgotten since the advent of closed-circuit fuel injection is that carburetors have float bowls which are vented to the open air. America has become complacent about smelly automobiles since today, they seldom get smelly - they just sit there.
However, we're driving cars with 1950's technology hidden within (I'm excepting you watercooled guys for this rant). If you remove the air cleaners and look upon the top of the carbs, you'll see a vent tube - usually 3/16"-1/4" in diameter, maybe on an angle, right at the top of the carb and usually just inside of the throat opening. There is nothing between that tube and the raw gas sitting in the float bowl. If it wasn't vented like that the gas would have a hard time filling and then exiting the bowl, since to get out it has to react to the slight vacuum changes within the carb venturiis (more on that in a post some other time).
OK, so you go out for a spirited run in your dashing Speedster and, just like riding a horse, you come screaming back into the garage and park and the engine is all hot and sitting in a semi-closed engine bay without benefit of the cooling fan and goes into what the mechanical engineers call "hot soak" and soars up to over 240 degrees. The gas in the float bowls may or may not begin to percolate and all that petroleum vapor has to go somewhere so it goes up the bowl vent and out into the engine compartment and then into the air in your 2 or 3-car attached garage.
Before 1990 or so, when almost every car except for the Germans and Japanese had carburetors, people just accepted the fact that sometimes their car would smell a little "gassy", especially if the weather was just right (like hot, muggy days or nights). The smarter designers at the various carb companies figured out that, if they moved the carbs away from a heat source then (a.) they would work better and (b.) the bowls wouldn't percolate and (c.) the car wouldn't stink up the typical American's, finished, pristine, attached-to-the-family-room 2 or 3-car garage and then into the house (completely unacceptable from the wife's point of view, but often OK with the husband (who seldom cares about that sort of stuff anyway, right?))
So there you go. If it's running OK and you have an electric fuel pump then you could turn on the key and try running just the fuel pump for a while and then check for leaks (run your finger around all fuel fittings and hose connections and see if it gets damp). If it has a mechanical pump you can do the same with the engine running - just be careful of spinning things that can bite you. If you don't find any leaks, then you can add vents, one-way valves and breathers and all that stuff, but you may never find that the smell completely goes away.
Or you can do like us "oldies" do - have a 2 or 3-car un-attached garage where the smelly car(s) won't stink up the house.
Gordon
The "Speedstah Guy" from Beaufort
Member NSRA
