gas tank vent line?

[kleedus]

i am replacing my 85 c10 gas tank with an older tank. my 85 has 3 lines out of the sending unit
fuel
return
vent to the charcoal canister
and the older tank only has fuel and return
how do the older tanks vent pressure threw the cap?

i want to get rid of the charcoal canister and that vent line but do not want my tank to pressure up and overflow the carb.
so i need to know how the older tanks vent or do they not vent. i can only think of them venting threw the cap from what i can see. maybe like a radiator cap designed to vent at a certain pressure. my older tank did not come with a cap so i am not sure if that is even right . i think its a tank out of a 76ish truck

 

[crazy4offroad]

I think what you're calling a return line is the vent line on carbed engines. I have mine run to a check valve style diff vent under the hood.

 

[kleedus]

my 85 has a 3/8ths fuel line and a 5/16th line to the pump then a line going past the pump across the frame and to the charcoal canister on the driver side so three total lines coming out of the tank


i think i will just get rid of the charcoal canister and put a vent cap on the core support

the tank has to vent air in as the fuel gets sucked out
and to vent pressure as temp changes and build pressure up or it will pressure up and over flow the carb and fill the engine with gas i had that happen to my jimmy it was a diesel and i put a 454 in it the tank was not vented right for gas

 

[Swims350]

3 lines is exactly right, one mina feed, one return, one vent.

the older ones curt is exactly right, one main feed one vent, NO RETURN our 76 was that way.

As for letting in fresh air as fuel goes out, I don't see that one happening, the cap on the charcoal can has a pressure valve that only opens when the pressure reachs that PSI. Any other time it's doing nothing. That's what i got from it anyways. I may be wrong.

I blocked many return lines, mostly because it seemed hard to restart the engine and the fuel would leave the filter, looseing prime. So you could use that 2nd line as a vent or as a return.

I would use it as a vent as it's meant to be used. I left mine open, breather caps work though, so either way.

Now on my 88 tbi truck I smell gas alot with it open, on dad's 84 and the 85 mcss I did the removal to I smell nothing.