Gas Tank Vent and fuel pressure

[bannind]

1967 289 - stock fuel system.

Or at least I believe the fuel tank is stock. The fuel tank has a filler hose and another orifice to the right of the filler opening to it that shoots up to the cap. I believe this is the filler vent. I do not have any vents or ports to the left of the filler opening - is this normal? Newer vented gas cap.

Short story long - any time I fill up with gas, I always make sure I do it before driving around for the day so I don't end up parking the bronco with a full to the brim tank. Any time I fill up with gas and immediately park it the gas fumes are horrible. I assume that is due to fuel expansion and such. Came home last night, 1/2 full tank and parked in the garage as normal. Woke up this AM and the entire house smells like gas station. Out in the garage, the strongest smell of gas is at the carb. When I remove the gas cap, there is a large pressure release and usual hiss sound.

Am I building up pressure in the fuel system and is it running up and going through the carb to try and release the pressure? I do not have a charcoal canister or the evap/separator bottle either. I have no problem stopping by the junkyard to pick up 2 donors. but I don't know if I could make them work without the added vents on the gas tank. I do not feel comfortable doing any work on the tank adding ports, so if it comes down to it, I am just going to buy a new one if needed. I would really love to be able to park in the garage, but until I resolve the gas smell - the bronco will be outside in the winter weather.

Thoughts/suggestions?

 

[xcntrk]

Welcome to owning a carbureted, zero emissions vehicle. ;D

There are 3 major sources of stinky combustion related odors. First is the fuel tank and the ability to capture and manage stinky raw fuel vapor. Second is how the engine is burning the fuel and odors that can come from improper combustion including a half-gallon of fuel sitting at the top of your engine (aka carburetor). Lastly is the exhaust stench from toxins such as nitrogen oxides and carbon monoxide.

For the fuel tank vapors, a charcoal canister is the best option to capture and retain vapor odor. You will need a means of processing the captured vapor by recirculating back into the intake. Several options and approaches here.

For proper fuel combustion; a perfectly tuned carburetor or EFI system is necessary to prevent rich fuel conditions which lead to raw fuel odor. Most lean toward EFI and with either a stock system or tuned custom system, proper air/fuel ratios can be achieved to ensure excessive fuel is not wasted in the delivery and combustion (extra fuel leads to more smell).

For the stinky exhaust issue; many are moving to high-flow catalytic converters simply to reduce the amount of toxic odor coming from the exhaust. This issue can be amplified depending on how your exhaust is routed, interior venting, closed/open top, etc. Catalytic converters are great for the environment, but hey they also clean stinky exhaust that often leaves one with a headache after driving a non-emissions rig (aka carbon monoxide poisoning!)

Good luck!

 

[DirtDonk]

1967 289 - stock fuel system...
...I do not have any vents or ports to the left of the filler opening - is this normal?

Yep, EB's did not get the charcoal canister/Evap system until mid-'70 or so. For yours, it's up to you to add one.
I'm not sure Ford expected anyone to be parking their EB's in the garage when they first put them on the market.
Probably an exaggeration of course, but back then there was not much done to utility vehicles to keep fumes at bay.

...Newer vented gas cap.

how new? I wonder if it's failing, or never worked properly to begin with?
Not sure how to test one, but someone might.

Any time I fill up with gas and immediately park it the gas fumes are horrible. I assume that is due to fuel expansion and such.

Very likely, but also could be due to a leak that you don't really see.
Some likely suspects are:
1. The tank itself. Maybe a failing sending unit seal?
2. The sending unit rusting out.
3. The filler hose leaking down at the tank.
4. Any of the rubber or plastic lines associated with the fuel tank.
5. You didn't say, but is there a secondary tank and selector valve?

When I remove the gas cap, there is a large pressure release and usual hiss sound.

Yeah, very common in fact, but not necessarily "correct" either. If you were to drive it then park it with the cap loose, I wonder if you'd have the same fume issue? It would still come out the filler neck to a point, but with no pressure built up, I wonder if it would be to the same extent.

Am I building up pressure in the fuel system and is it running up and going through the carb to try and release the pressure?

Very likely. Two common areas for it to escape a carb are the bowl vents (and then out the air cleaner), and the ends of the throttle shaft.
Do you see any seepage at the base of the carb that could be leaking shafts? Or perhaps a leaky gasket?

Good luck. I would certainly try to add an evap system, but since you said you are not likely to mess with the existing tank (and for good reason!) then yes, it would require acquiring a different one.
Definitely use the canister from a newer rig ('76 or newer trucks, and about '74 and newer cars I think) so you can mount it up high and not have to use that secondary condensing tank behind the driver's seat. Just a high mounted canister and a few hoses/lines would be all you need.

Not sure how nice they play with the older style gas cap, but someone might know. Ford went to a completely different design cap in '70 when they added evap to the fuel system.

Paul