How can I trace fuel smell.

Try a cigarette lighter.

When it goes "Boom!" you've found it.



Seriously though, good question.

 

Two years ago I can across a similar situation. Once I parked the car for the winter season I checked the lines visually and couldn't find anything. This spring season when I fired her up, the smell got stronger - took her for a small drive around the neighbourhood and let it sit in my driveway for a while running. It was then I noticed one of the fuel lines being damp.
Seems it maybe time to do your fuel lines - change all if them, don't just change just the culprit.

 

Is it gas or exhaust. Have you check to see if any of the carbs are leaking or are wet on the outside. Do you smell gas several minutes after you shut down the car. Is your vapor recovery system in tact. Are all gas lines dry. Check exhaust for leaks. Look at sample port tubes to make sure they are not cracked or rusted out.

 

The fuel tanks leak as well, so check those carefully.

 

I had the same issue a few years ago. I traced it back to the part/union in this picture that connects the three fuel lines together. It had developed a crack which allowed gas fumes to buildup in the garage.
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I have a similar issue too, found it to be the hoses that connect the 2 tanks below. Ordering a new set from SRI Monday when he returns from out of town.

 

Also known as a "sniffer". There are many types available, most are similar to what we used on the F-15.

Combustible Gas Leak Detector | eBay
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Change the fuel lines, the new gas just eats the old lines like a Thanksgiving dinner. Takes about a day, but well worth it.

 

Let me offer my .02 cents: What changed?
if you haven't done a major or gas filter change or messed with any hoses, then I'd say some fuel line cracked somewhere or fuel pump or accumulator is showing its age.

In my case, it was a major about a year ago and all hoses were replaced. Hence it was more likely a hose clamp was loose. And so it was, the vent hoses on the top of the right fuel tank didn't last.

 

The gas in the float bowls will evaporate, especially when your car is hot just after a drive. My car has a flapper on air box that closes when hot and off. It makes a noise when I turn the car off as it closes.

Does your car have that?

 

If one has an FI car, change ALL the plastic lines too. All. Of. Them.

Just because they "look good" doesn't mean squat. Don't bother asking how I know.

A member here makes a good kit to do the job. And it ain't expensive. No affiliation.

 

My Carb 308 has a stronger smell when I use gas with ethanol which is more prone to evaporation.

 

It's a Euro carb car without any vapour recovery system or similar things. Or without flaps in the airfilter box.
Like scowman already mentioned, it just has four carburettors in the middle of the engine V filled with fuel which heats up after a drive. Just sniff on the passenger side intake and you will smell where the fumes come from.
I fear you will have to live with that with a Euro carb car.

Best Regards from Germany
Martin

 

All carb 308s tend to smell of gas when park in a contained unventilated space. 40 years on, I would have to assume that even with cars equipped with the flaps on the air box, they probably aren't working as designed anymore anyway. Is this a new car to the OP? Otherwise something has changed that is causing the more pronounced fumes.

 

Refill/renew, or replace the charcoal canister, that vents to atmosphere.