1970 non-vented gas tank

[Mark #44888]

I want to make sure my fuel system is correctly configured.

I have a '70 non-ec L46 car. Feb.20th build date.

Non-vented gas cap. One return line that runs parallel to the supply line.

Is this functionally okay, or is there supposed to be some kind of venting?

The tank has the valve on top of it and I'm not sure if that's for bleeding vacuum or pressure?

I mistakenly used a non-molded piece of fuel hose from the body to the pump, and after about an hour, it collapsed; I assume from the vacuum and the heat from the engine (and also maybe too short of a piece).

I just want to make sure it's okay with a molded piece. Thanks -Mark

[Terry M.]

Re: 1970 non-vented gas tank

There is/was a molded fuel line available -- but it is not necessary. The original fuel hose from the pump to line on my 1970 LT1 was not molded. It does have to be long enough not to kink, though.

Gas cap should say SEALED. The valve on the top of the tank should be the vent -- if it is working correctly.

With a fresh -- that is not 30 years old -- hose from the line to the pump if it collapses loosening the cap should allow the hose to expand -- if vacuum in the tank is an issue. My guess is the short hose just kinked after a bit. Try again with a longer hose.

[Paul O.]

Re: 1970 non-vented gas tank

Mark the "S" molded hose is the way to go with a base motor car because of the angles that come into play with the feed line and the fuel pump inlet. The check valve on the gas tank is it on the right side and does it go to a charcoal canister if it is it work kind of like this when the engine is running vacuum draws vapors to the base of the carb through the vent line and canister when the engine is not running the charcoal is absorbing the vapors and if the fuel tank is over serviced or the car is tilted to the left there is a floating ball in the vapor seperator that prevents fuel from making it to the canister. Paul

[Jim T.]

Re: 1970 non-vented gas tank

Mark I am a original owner of a 70 and I have never used a molded replacement gas hose, just bought the gas hose in length long enough to work. Do the same with my 68. The non vented gas cap on a 70 should give you a audible indication of pressure in the tank when you remove it. This is normal. I do not have the fuel vapor CA required system on my TX bought 70. Two parallel lines to the gas tank. Maint check for you is to check the cracking of the two fuel hoses that go from the lines to the gas tank. The fuel return line will be more difficult to change than the supply hose.

[Joe L.]

Re: 1970 non-vented gas tank

Mark------

If by "valve on top of the tank" you are referring to the round, half-dollar size, more-or-less "flat" device about 6" to the left of the filler opening, that device is a pressure/vacuum valve. It functions BOTH to relieve pressure and vacuum. It replaces the same functions which used to be in the cap for 63-69. The valve does not relieve at ambient pressure, though, nor does it relieve vacuum at low vacuum levels.

[Mark #44888]

Re: 1970 non-vented gas tank

Thank you all for the replies; I feel better about it now, knowing it's not going to blow up

I had recently replaced the rear hose connections when I installed the new gas tank. I went ahead and ordered a molded one for the fuel pump, and will give that a try.

Happy Motoring ! (an old Humble gas slogan I think)

- Mark