gas tanks venting

[hiball3985]

highball, wouldn`t the act of filling up the tank, allow any pressure during the filling process to just come out the filler tube ? After all, the gas pumps nozzle is considerably smaller than the opening in the filler tube.

Well yes and no, depending on where the filler neck is located and I don't remember on the cars. Here in Calif the fuel nozzles have a big stupid rubber grommet type thing that seals off the filler neck so that fumes don't come out.
After the fuel reaches a certain level the filler neck will be blocked and no way for the air to escape without a vent. Or it would just force fuel back out the neck.Just my opinion.

[RICH MUISE]

Missed the replies on this until this morning. My venting issue was pretty much self-inflicted I believe. A stock reproduction tank, but:
1. I did not use the oem vent location
2. The vent location I did use was on the in-tank fuel pump flange which was located on a recessed box at the front top of the tank
3. my car has a california rake
4. the tank itself was mounted with a 1/2 or 5/8 nylon spacer bar at the front top so I could clear the fuel lines around the floor support, giving the tank it's own rake.

all of that was adding up to the vent outlet being under fuel level much longer until I used up enough fuel. Gas would get into the line and start a syphoning effect.

the problem appears to have been solved finally. I installed a check valve on the vent line close to the pump and drilled a hole in the gas cap. I took the car on a 750-mile road trip this past weekend, and filled up the car up 3 times. I never had pressure buildup at the cap, nor gas spewing from the vent line.
Temps were in the mid 90's, so I think I'm good to go!
Jim. the one-way check valve was less than 10 free shipping. I can dig up the eBay ad if anybody wants it.

The pic.......I left a section of hose there in case I needed to pull the check valve while on the road. Note I have the arrow on the valve pointing to the tank. This allows air in, but not gas or air pressure out, thus the drilling of the cap. In the pic, the strip of sheetmetal at the top of the pic is the flange on the floor support (I told ya it was close, lol.). You can also see the insulation sheeting I used as a "rub pad" on the top of the tank. You can also see a lot of road grime!