What's causing this gas smell?

[Rickety Rhino]

I need help diagnosing a gas smell. It fills the car, mainly on hot days,
especially when driving up several thousand feet into the mountains.
I don't ever smell gas in the engine compartment. I sometimes get vapor lock,
which never happens with my other Tercel.
Gas leaks out the gas cap on hot days just sitting in the sun if I've filled up
recently. I hear and smell a good hiss when I unscrew the gas cap, but my
other Tercel does this too, with no gas smell problem. Does that mean my gas tank
is OK (no leaks?)
Things I've done: replaced the charcoal canister twice (they all sometimes passed,
sometimes failed the repair manual tests). Replaced the fuel pump.
I've tested that the vent and return pipes are clear between the canister
or fuel pump and the inside of the gas tank (with gas cap off, I can smell when
a bike pump pushes air through either pipe).
The carb float level often looks a bit high, but since I never smell gas in
the engine compartment, that wouldn't be the cause, right?
I plan to install a new carburetor float, and am considering making my own
charcoal canister, since I've had no luck with used ones. Does anyone have
experience with that?

Thanks for any help!

[Petros]

have you tried replacing the gas cap? My daughter's CRX had this problem, the vent in the cap was bad, and replacing the gas cap solved the problem. Also make sure the lines to the charcoal canister are connected properly, switching them will cause a fuel leak.

Also, on the back side of the carb (the firewall side) there is diaphragm that always leaks out and drips on the heat shield. YOu can see the stain on the heat shield if this is the source. Several of mine did this and it is annoying. Not much of a leak, but it does not take much, it seemed worse on hot days.

Good luck.

[Rickety Rhino]

Yes, I've replaced the gas cap twice, and the canister hoses are routed the same as on my other Tercel which doesn't smell. Since there's no gas smell near the fuel pump, I don't think a gas leak there is the problem.

[ARCHINSTL]

How about a leaky rubber tube going into/exiting the tank? I replaced mine back in '05 as all three were OE and were quite cracked - although I did not note any gas smell.
Another source, while probably far-fetched would be a leaky filler tube - there have been reports of these being perforated (some are corrugated, so can harbor crud) - there are some old threads on this.
Another really out-there source could be from a loose/perforated sending unit cap.
There are lots of places where these fumes can enter the rear of the car.
Tom M.