Jere Urso

Whenever I go for a long drive, when it's hot out, my tanks builds up pressure and releases when I take the cap off. Is this normal? It was pretty aggressive today and my car flooded after that at the gas station lol

Laf12

SAME THING HAPPENS TO ME!

If you looked at the gas cap it says something like "not vented". When the pressure build up in my tank it makes a very annoying hissing sound so I only put the cap on half way. I'm thinking of drilling a small hole in the top of the cap to release the pressure. I would also like to know why this happens and if there is a permanent fix.

DreamInRotary

iTrader: (49)

Do either of you have your charcoal canisters installed in the engine bay? If that is removed the system will build pressure and the tank will pressurize. You can bypass this and just vent the small line to atmosphere and it will cause the system to not pressurize. It's a tiny line that runs in the engine bay on the firewall near the two fuel lines and should go to a can on the passenger's side strut tower.

Jere Urso

I still have the charcoal canister, do they go bad?

t_g_farrell

iTrader: (1)

So yeah, you need to vent the tank. That is usually done by the vent line that comes up into the
engine bay and into the charcoal canister. The canister either is integral to the top of the air
filter (for SAs) or its a canister near the carb. If the canister is not working right it won't allow the
pressure to release causing this kind of thing. Very common to have this after a rats nest
removal and capping off the vent line. I have my vent line plumbed into the nipple on the middle
iron below the oil fill tube and have a pcv valve plumbed into the oil fill tube nipple and that
goes to manifold vacuum. This will control pressure while driving and allow some relief if sitting
in the heat for awhile. Also cures lung butter in the oil fill tube.

Jeff20B

iTrader: (13)

t_g_farrell, I was having the same thought about plumbing my tank vent line to either the nipple on the intermediate iron, or the oil filler nipple. I get a good amount of pressure in my tank and right now if it's not vented to atmosphere due to my charcoal canister not working anymore. It's like clogged up or something. I've gone through two of them in only two years so something is up. Must be the more active GSL-SE send/return system producing more gas fumes.

My question for you is, is it ok to have your engine's internal air space filled with gas fumes? Has it caused any problems?

t_g_farrell

iTrader: (1)

None that I can tell. Besides, as soon as the engine starts it will pull them out of there via the
pcv valve plumbing and into the intake where you need it.

DivinDriver

iTrader: (15)

The charcoal canisters can plug up over time, yes.

7aull

iTrader: (2)

My SA does this also (stock) - and I just ease off the cap at fill-up time. I guess what I would like to know is - so what? Car seems to drive fine. Is this creating a problem I should be watching for?

Stu Aull
80GS
Alaska

t_g_farrell

iTrader: (1)

Its just not right, damn it Jim, err I mean Stu!

Probably not, the pump acts like a regulator in this case and the return line has a restrictor to
keep the pressure from pushing gas back into the carb.

Besides your polluting the alaska wilderness with your hydrocarbon effluence.

LongDuck

On other, newer cars some pressure is preferable in the tank to help the pump overcome pulling against a vacuum. The charcoal canister is there to grab and hold any fuel vapor when it's sitting until you go to start it up, at which point the intake vacuum sucks the vapor out and into the intake where it's burned - drying out the charcoal canister.

I've always had pressure on fuel cap removal, and never thought anything of it. Also never had any problems with 'lung butter' in the oil fill tube, but my SE is running a full rat's nest - I have emissions testing where I live.

Glazedham42

iTrader: (4)

Bringing this back from the dead TG and Jeff. Just wondered how this tank vent setup was working for you guys now several months later? I am thinking about throwing my charcoal can in the dumpster and just running the fuel vent line from my fuel tank straight to the intermediate iron. I'm trying to have an ULTRA spartan engine bay on this car. ONLY what is really absolutely needed.

Doing this will allow me to get rid of:

1) The charcoal canister
2) The hardline on the firewall from the charcoal canister to the intermediate iron
3) Several feet of hose and clamps

TG, what did you do use to adapt the tiny tank vent line up to the size of the intermediate iron nipple? Just a really stretchy piece of fuel hose? They appear to be quite different in size to me.

Jeff20B

iTrader: (13)

As a temporary test, I used one of those plastic things you get with a reman master cylinder, meant for bench bleeding. It easily adapts the 3/16" vent line up to the 5/16" hose. The hose is routed down to the plastic elbow between the air filter and turbo inlet. Seems to keep raw gas fumes from being noticed unlike the way it was before, with just an open vent line constantly spewing.

I ditched my charcoal canister when it got clogged. Glad it's gone.

How do I like the current setup? Not sure yet. I'm getting water condensing up under the cap so I drilled it with a 5/16" bit. The nipple on the side was left open with a short length of upturned hose to keep oil in when you do an oil change, and to try to get a chimney effect which you wouldn't get at all if it was simply capped off. The result is I still get water condensing, but not as much as before the hole was drilled. And it does dry after a while which it couldn't do before. Of course the weather has turned cold around here and I've only done short drives to test carbs.

j9fd3s

iTrader: (3)

why not put a charcoal canister under the car? that way you run the hoses like you want, but the canister is there.

t_g_farrell

iTrader: (1)

So the way mine is setup, I have the vent line going to the oil filler tube nipple, just used hose
that fits the vent line and forced it on the nipple. I then have the vacuum line with a pcv valve
attached to the nipple on the iron.

BTW, in my previous post I had misstated which line was hooked to which nipple. Sorry about that. Probably doesn't make
a huge difference either way.

Been working great for years now. Never have lung butter.

Glazedham42

iTrader: (4)

Thanks for the info TG. Do you get any bad fuel vapor smells in your garage or around the car when it sits for a few days?

I think I'm going to try your setup. Just want to get a better idea of what to expect once I do it. I have always hooked up my PCV the way you describe and it works great. No lung mustard at all in the fill tube.

t_g_farrell

iTrader: (1)

My wife complains about it smelling when I come back from a run, but I think its all just exhaust as it
goes away after an hour or so and doesn't smell at all until I start the car the next time.