70 fuel tank venting question

18436572

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How on vettes "without" EEC but with a factory installed sealed cap does air get into the tank when fuel is removed? The small vent built in the top of the tank only allows pressure "out" ---(unlike the valve in the 69 and earlier vented Cap which is a 2 way valve.)
 
NO EEC has to have a vented cap, typicaly, from what I hear....

my '72 had EEC/charcoal canister on it, and so that 'separator/float valve' on the upper driver's end can sometimes get hung up and leave pressure in the tank.....not a issue with a carb on the thing, but with my DPFI....I can drive for something like 1/2 a tank and there be pressure in there....

the valve hangs up in the closed position form the higher fluid level, meanwhile the tank is warming, even though the level drops, the float ball hangs up with pressure.....and so no vent....PIA...don't happen all that often so I don't worry over it....

:crap:
 
NO EEC has to have a vented cap, typicaly, from what I hear....
I would think it needs a vented cap also but the parts books say they take a sealed cap and I understand they came from the factory with a sealed cap.I was told by a buddy his NCRS book says it must have a sealed cap.Quanta also says they take a sealed cap.So how does the air get in? I doubt the return line can add air.:confused:
 
NO EEC has to have a vented cap, typicaly, from what I hear....
I would think it needs a vented cap also but the parts books say they take a sealed cap and I understand they came from the factory with a sealed cap.I was told by a buddy his NCRS book says it must have a sealed cap.Quanta also says they take a sealed cap.So how does the air get in? I doubt the return line can add air.:confused:

ANY car without a EEC charcoal canister type arrangement, HAS to have a VENTED CAP or some such valve to allow airflow in/out of the tank....

I was referring to my '72 wit the black plastic thing that has this seldom seen fault with the sticking ball, allowing pressure in the tank to go positive....noticed to varrying affects when I go fill the tank just off the freeway....overnight, the affect is less....obviously, as the gas cools off....

from what I read above, the parts books are RONG.....that much I remember from many earlier comments over the years....the only cap listed these daze for our tanks is the sealed cap meant for the EEC/canister system....

:gurney:

OH, to vent the caps for use with your car, I would just drill a 1/32 hole in the cap, and tap the edge inside that goes against the center spring loaded piece....tap that edge down a hair in one spot to allow gasses to escape....

NOW, having said that, you maybe get some fumes in your garage from that....

but that's same as any old car....vague gasoline smell....my wife is allergic to it, so it's a sensitive topic with me....had to go to extra lengths for that reason...attached garage....
 
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NO EEC has to have a vented cap, typicaly, from what I hear....
I would think it needs a vented cap also but the parts books say they take a sealed cap and I understand they came from the factory with a sealed cap.I was told by a buddy his NCRS book says it must have a sealed cap.Quanta also says they take a sealed cap.So how does the air get in? I doubt the return line can add air.:confused:

My 70 takes the sealed cap. It also has the return line. Maybe the pump has some sort of vent? I have one here and it has holes in different areas of the top part.
 
NO EEC has to have a vented cap, typicaly, from what I hear....
I would think it needs a vented cap also but the parts books say they take a sealed cap and I understand they came from the factory with a sealed cap.I was told by a buddy his NCRS book says it must have a sealed cap.Quanta also says they take a sealed cap.So how does the air get in? I doubt the return line can add air.:confused:

My 70 takes the sealed cap. It also has the return line. Maybe the pump has some sort of vent? I have one here and it has holes in different areas of the top part.
Yes thats what everone says the car is supposed to have.I understand that if you have a 70 and get it judged the NCRS judges will dink you if you have a vented cap.I would think that if the system was tight and you were at cruising speed you could run the risk of the tank crushing internally from the vacuum.
The fuel pump has some holes in it to vent the movement of the of the back side of the diaphragm but those holes shouldnt be exposed to the fuel.
 
You know, it's quite possible, that it was an oversight by GM, and that there was a recall/dealer fix. It HAS to vent somehow.
Having a car inoperable for judging purposes is..........................:crap:
 
You know, it's quite possible, that it was an oversight by GM, and that there was a recall/dealer fix. It HAS to vent somehow.
Having a car inoperable for judging purposes is..........................:crap:

Early tanks vented via the cap...case closed, smell up the garage under certain circumstances....like a warm weather front comes through and the temps rise, forcing fumes outta the tank.....

when my '72 was stuck out there it came with that charcoal canister tank....it vents to the air stream above the throttle body/choke.....with another line going to that silly valve that stops the gas outta the vent line....but if the tank tries to go negative, air can go right back in through that one way check valve...mounted on the top drivers end.....the most amount of negative it can attain is due to the slight vacuum with the engine running, in the induction air stream AFTER the air cleaner....

the only time it's possible to go positive, I have found....is that IF that float ball plugs the vent line going forward to the canister.... to stop gas from getting there....and summer heat keeps pressures up, the thing CAN stay closed, while the tank being warmed from extensive driving manages to create air/gas/fumes pressures enough to keep the check ball closed....so then I pop the lid and some gasses escape.....I have had it even hold pressure overnight....not a LOT, but enough that I notice it....and seldom enough to know it's not a real problem....

one thing I did note however, is on my '87 C4 vette.....I had a mysterious fuel smell on a fairly constant basis....never could find it....so got it on a lift one evening with the vette club...and went determined to find it...sure enough there was this fan of tiny little lines there, kind of like fingers on my hand about 1/8 inch diameter.....I have NO CLUE WTF they accomplished...but in that fan of lines...ONE of them had a rotten coupling hose...and that was what stunk....and so replaced it and the problem was solved until I sold the car.....

:crap: curious as to what was on the GM guys mind with that configuration, I have no clue....

:fishing::surrender:
 
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