Fuel Tank Venting Issues

[cv70chall]

I have recently replaced my tank with a non-1970 model (My car is a 1970) and there is no vent tube on the tank itself. There is however- a set of two tubes on the sending unit (I know the larger one is the fuel line). The filler neck also has a small nipple on its underside and I believe we may have run the line from the top of the filler neck (behind the fender) to that smaller nipple on the sending unit. I think this may be wrong.
Should I simply have the tube from the filler neck hang down behind the fender/ chassis as overflow? The existing gas cap is already a vented cap.

Thanks

[Chryco Psycho]

the second line on the sender is the return line & only the 3/8" sender has the second line .
 Factory had a line that drained down into the frame rail from the filler neck but it will work fine if you connect it to the sending unit , as you say the cap is vented anyway .

[cv70chall]

Weird part is- I notice at start up the fuel filter at the carb (glass) is full. As the car runs- after about 5 minutes, the fuel level in the filter drops to about 1/4 full. Is this normal or have I got an issue?  Should I make the small vent hole in my gas cap slightly larger?
I seem to have plenty of fuel pressure and I plan on replacing the fuel pump with a fresh one just to be sure.

Thanks

[brads70]

Weird part is- I notice at start up the fuel filter at the carb (glass) is full. As the car runs- after about 5 minutes, the fuel level in the filter drops to about 1/4 full. Is this normal or have I got an issue?  Should I make the small vent hole in my gas cap slightly larger?
I seem to have plenty of fuel pressure and I plan on replacing the fuel pump with a fresh one just to be sure.

Thanks

I'd strongly  suggest getting rid of that glass fuel filter!  Fireball waiting to happen IMO  I've had them rattle loose before and glass breaks easy 
You can buy a vented gas cap and not worry about it?

[cv70chall]

Yikes! Really?
Can I get away with the OEM style filter down low and not run this second one then?

[brads70]

Yikes! Really?
Can I get away with the OEM style filter down low and not run this second one then?

I'd say so. One of those common  parts store steel fuel filters?

[BIGSHCLUNK]

 

[Chryco Psycho]

I doubt the lack of gas in the fuel filter is caused by a non vented gas cap , run the car with the cap off to be sure , as long as the carb is full it really doesn't matter how full the filter is , but i agree about losing the glass filter

[cv70chall]

Ok, so now I'm really stumped. We did some adjustments on the carb, set the timing correctly and checked all voltages/ outputs just to rule out anything being electrical.
She ran great all last week- and then today- same thing. Would not start- and when it did- quickly died and then I had a backfire from the carb. No issue with venting as the rear cap is fine after checking that too.
Have a fresh tank of gas so thats out.
The only other thing I can think of as a maybe would be the fuel pump- so I'll change that out this weekend.
But after that if I'm still having issues what next?
??