Gas Tank Breathers
 

Well, I have the same issue that a few other guys have had which is that I've got a new tank in my '70 K5 all hooked up and functioning properly but I don't have the charcoal canister setup at all and when I fill up, I get gas spilling out from underneath the truck. My issue is that the breather lines are way too short (like about 12" each) and so when gas gets going out of one it pretty much has a siphon effect and keeps on pouring. I want to solve this by running longer vent lines but I'm not sure where to run them to (where to mount the other ends) and what breathers to put on the ends of them. Anyone willing to post a few pics of where their gas tank vent lines bolt up to the frame or elsewhere? Any ideas would be much appreciated!

Re: Gas Tank Breathers
 

Do you have this set-up at the rear on the opposite side from the fill neck?
Attachment 1550597

My '70 has this but also has about 4 or 5 rubber lines directly below it under the bed.....I filled it up and gas started pouring out...all of the rubber was dry rotted and cracked. I replaced them and that stopped the leak(s).I do have the EVAP canister but I still haven't figured out what all these lines are supposed to do?

Re: Gas Tank Breathers
 

That's an interesting looking apparatus, If I had to guess I'd say it has to do with the EVAP but it'd be just a guess. All I've got coming out of the tank other than the filler tube, sending unit wiring and fuel lines are the vent/spillover tube that runs up to the gas filler inlet and then a breather on both the drivers side and the passenger side.

Re: Gas Tank Breathers
 

For sure........I've been to two world's fairs and a goat f***in and I've never seen anything like it....:lol:
I suppose that some '70s had an EVAP and some didn't....I always thought that the pollution stuff didn't really start until '72......? but I've been wrong before..

So which line is the fuel coming out of?
I would tend to think you need some kind of rollover type vent...

this is interesting because I'm getting ready to fab myself a larger tank with an EFI set up.....
I'm not sure if I need to retain that jungle gym back there or just get rid of it..?

Re: Gas Tank Breathers
 

Yeah, I learned something new too ! My 70 doesn't have those vent tubes on the opposite side. My vent tube exited right by the filler neck, which would make the tube about 3 feet long. I tried to post a pic but couldn't find one, sorry.

Re: Gas Tank Breathers
 

My 71 Jimmy has a replacement tank installed by PO. Don't know what filler neck was used. I put new rubber vent lines which run to a "collector" next to the filler. Four lines in, one line out. A single line would go from there to the front canister under the battery which I do not have. The single line goes thru the floor and stops. It is open and clear. It takes forever to fill the tank because I must run the gas pump at slowest possible rate or it clicks off. I hope this info is helpful to someone and if anyone knows why mine won't take gas, I'd like to know. I suspect the filler neck?????

Re: Gas Tank Breathers
 

Funny I am just getting to this part of the project also and my hard lines to the vent stack on the drivers side are all rusted out. Has anybody had problems with just running a vented cap and plugging all the other vent tubes except for the filler tube breather??

Re: Gas Tank Breathers
 

That's exactly how they come from the factory when there's no emission controls, vent pipe and fill pipe.

Re: Gas Tank Breathers
 

Thanks Hemi43 I wasn't looking forward to replacing all those steel lines that had rusted out on me!

Re: Gas Tank Breathers
 

NP !! Just remember to run a vented cap.

Re: Gas Tank Breathers
 

Never saw that on my 70.

Re: Gas Tank Breathers
 

@A1971blazer:

Hahaha, yeah I don't like not knowing what something does or why it's there so I'd be looking for any way I could to pull that contraption off while doing the EFI conversion. The fuel that leaks out of mine comes from those breather lines because they're so short that they just lay over on the leaf spring at about equal height as the tank which just seems incredibly dangerous. If I park the thing on a steep hill I get gas running out, which is just like crossing your fingers that no passersby toss a cigarette out their window and burn my blazer to the ground... I think you're right on using a rollover breather but I'm wondering if I need to mount them as high up as the gas filler cap is-I'd guess so.

@4oldcars:

I read on some way older threads that the slow fill problem is usually because the previous owner didn't use the filler neck from the old tank when they put in the newer tank and the bend the gas filler tube has to make to go around the body mount if they don't use that old filler neck is so sharp that it causes the filler tube to fill up before gas can get in the tank.

Re: Gas Tank Breathers
 

I don't think the lines should just go to nothing...I suspect that perhaps something has been removed and the lines were just left there.
Here are some pics of a '71 fuel tank set up on a truck that I dismantled....it has 3 tank vent lines that sorta interconnect and I suppose one leads up to an EVAP....?

Again this is a '71....the vent lines are on the driver side and go up into a device (rollover vent) inside the vehicle adjacent to the filler neck....
on my '70 they're on the passenger side going into that device (on the picture in the post above)

(rear of vehicle..... looking forward)
Attachment 1551580

Attachment 1551581

Attachment 1551582

Attachment 1551583

Re: Gas Tank Breathers
 

Nice, thanks for the pics. Yeah I'm sure mine used to go somewhere, they just aren't anymore. I think I'll just get some rollover vents and mount them to the inside of the frame rail and be done with it (unless it keeps leaking gas).