help me understand fuel venting please

[benno440]

just chasing some info on venting in the fuel tank, 68 charger factory tank, it has a lockable gas cap and on the fuel pickup it has 2 tubes one for the outlet to carb and the other smaller diameter hose runs up the filer neck to the gas cap i am guessing this is the vent line.

i have just welded a bung into the filler neck for my -4 an return line from the regulator.

the later model b bodies have multiple vent lines am i right?

the single vent line on my car is the sufficient venting? for my 450gph fuel pump?

when i primed my new fuel lines i put a rag in the gas cap and put the compressed air into it after a min or so when i stopped the pressure was so high i neally knocked myself out, is this right?

if i do need more venting what would you suggest?

thanks in advance

 

[watermelon]

not sure if this helps or not, but i am in the middle of doing an MSD Atomic EFI upgrade. i ran new supply/return lines to a new gas tank in my 66 Coronet and also am installing an eletric fuel pump from Tanksinc. 255 model.

i have my tank vented throught the gas cap (guess it came from the factory like that). however, i added the device from the link below in between the gas tank and gas-neck vent tube:

http://www.fuelsafe.com/store/vent-check-valves/tpv6-in-line-pressure-relief-vent-valve.html

here is the link to the oem of the product: http://www.newton-equipment.com/tpv6.html

i bought it from the fuelsafe.com website.

the device allows gas fumes to pass but will shut if gasoline tries to pass. it allows air into the tank when the gasoline level drops so the tank doesn't deform. also, if car is out in sun on a hot day it allows air pressure out of tank.

i may not even need to tie it back in to my gas-filler vent tube. i could probably just cap to outlet with an air filter of some type.



watermelon

 

[coloradodave]

If I'm understanding you, if you put your air nozzle in the tank filler tube and then stuffed a rag around it to effectively seal off the top of the tube, then it would figure that the compressed air had nowhere to go. Have you tried leaving the cap OPEN and then cranking the motor over to see if you get fuel out of the carburetor side of your fuel pump? Did you check to see if your pump needed to be primed? Fuel cells are usually vented with a -6 fitting, which has a pretty small inside diameter and that doesn't seem to impede flow on a race motor.

 

[RustyRatRod]

Simply run a vented gas cap.

 

[tpodwdog]

fuel tank venting does one thing.....keeps the pressure in the gas tank at constant atmospheric pressure. that means the air pressure inside the tank is the same as the air pressure you are standing in right now...which is 15 PSI . my '66 has a tube easily seen in the trunk for this.....my 70 Road Runner does not and vents through the gas cap . with inadequate venting , your fuel pump would suck the tank and collapse it......ORRRRRRR. when it gets hot outside..it will blow it out and puff it up. it works on displacement....if something goes in....something must come out and visa versa. it just lets the gas tank "breathe"

when i told you to do the rag/air hose trick....the "in" line should have been removed from the fuel pump on the engine. this would prime the fuel lines from the tank, to where you need the fuel...at the carburetor preventing you from having to crank forever to get fuel to the fuel pump. once fuel came out near the engine it should have been re-connected.

are you using an electric fuel pump by chance ??

 

[benno440]

tpodwdog, welcome back. i have a mechanical, it flows 450gph thus why i also rn a regulator. i did what you said by removing the in line to the pump and then when the fuel came out i put it back on.

rusty, do you know if they make a vented gas cap for the 68 charger? is my cap not a vented one already if the vent line runs up to it from the tank?

 

[RustyRatRod]

What I am saying is there's no need to run a vent line. Just buy a vented gas cap. I don't know if your cap is vented or not. I'm on the other side of the world.

Vented gas caps are super easy to make. All you need to do is drill like a .100" hole in the cap in a spot where it will not allow moisture in, but will allow it to breathe.

 

[watermelon]

lookie what i found on googler images:

http://www.goodmarkindustries.com/p-10201-gas-cap-62-70-mopar-wo-ecs-64-70-gm-wo-eec-vented-70-amx-javreb-wo-cal-emis-2130-757-621.aspx

i bought a vented cap at a local auto parts store.

 

[5.7 hemi]

450gpg pump......that's alot!!!!