Fuel Sending Unit vent blocked?? Fuel Cap help?

[Fgill]

#1 previous owner blocked ( 3" section of hose with clamps & a bolt) this little tube that comes off the factory fuel sending unit.
I believe its the vent, is this correct?
Q is - should/why would this be blocked? and by being blocked is it creating a syphon/fuel drawing issue to the engine?
if its not ment to be blocked, where does this tube lead to?

car is a 71 demon and still has the evap system in the trunk, but not sure much if any is hooked up still.
#2. Gas cap is unknown chrome aftermarket crap.
cap should be a non vented correct?
car seems to be starved for fuel....
any help here would be appreciated...Im a lil confused whats what..or what should be.

 

[67Dart273]

The sender port was NEVER the vent and in fact is not factory

up through 69, and the 70? or 71? which did NOT have evap/ cannister, the vent was a tube hooked into the filler pipe

The evap vent varies. Some early years had a separate vapor separator can in the trunk. Somewhere? around? 3-74 Ma went to a separator right in the tank, so the tank had a separate vent connection

If you download the correct year service manual from MyMopar (they are free) the routing of the vent system is detailed.

If the previous owner blocked any of that you need to identify the fitting that used to run up front and open that up. It needs to either go up front as original, "up high" so it does not siphon, or ditto, in the rear. Without routing it up into the trunk and back down, not sure how you would do so

Your other option is to remove the filler neck and weld / braze/ etc a fitting in so you can duplicate the 69/ earlier system.

No caps were vented in these girls. if you run a vented cap you run the risk of fuel down the fender

 

[Fgill]

Thanks 67dart273.
Car is a 71 and it still has the evap tube in the trunk. PO cut, blocked and mixed up all sorts of stuff, so making sense of it has been a challenge. I dont have access to the proper routing diagrams but will attempt to locate. thanks again.

 

[67Dart273]

Easy. Go to MyMopar. There are several service manuals there, and some of them came from the guys right here. Sometimes you have to download Plymouth vs Dodge and vise versa

Free service manuals

MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

Looks like what you want is the 71 Plymouth service manual. Read both the emissions and the fuel chapters

 

[Fgill]

I did attempt to find the actual line routing diagram in the onine manuals for 1971, cant seem to locate the precise one, but ill keep digigng. thanks for the links.
I am getting mixed results in what I did find..some info states its a return line (2nd spout on sending unit) still unsure if its ok for it to be plugged off or not.
I do understand OEMs didnt have it, so it may well be a non-event that its jerry rigged closed off.
"if" hypothetically speaking though, my fuel system has been all closed off by PO (no venting, return line capped off, gas cap sealed tight,etc) this would by way of physics, create a suction issue when the motor tries to draw fuel from the tank wouldnt it?
like trying to pour gas out a gas can without the vent open..the fluid locks up and comes out in spurattic gulps...
am I over thinking this? lol

 

[67Dart273]

Right. You MUST have a vent. The problem is if you take the original fitting from the tank/ separater and just leave it open back to the rear it MIGHT siphon. If the factory separator is in the truck you are likely OK so far as siphon goes, that is it's job.......to separate liquid, drain it back, and allow the vent to "vent."

There should be a drawing in the manual, either in the fuel/ tank section (9?) or the emissions section (24? 25?)

 

[RedFish]

"if" hypothetically speaking though, my fuel system has been all closed off by PO (no venting, return line capped off, gas cap sealed tight,etc) this would by way of physics, create a suction issue when the motor tries to draw fuel from the tank wouldnt it?
like trying to pour gas out a gas can without the vent open..the fluid locks up and comes out in spurattic gulps...
am I over thinking this? lol

A bottle gulps in air through its only opening. That's your sporadic flow. If all tank vents were closed and you were creating a vacuum in fuel tank, fuel flow would slow to stopped. No where for air to go in.

 

[famous bob]

A bottle gulps in air through its only opening. That's your sporadic flow. If all tank vents were closed and you were creating a vacuum in fuel tank, fuel flow would slow to stopped. No where for air to go in.

I replaced my stock tank when I started building my 68 fastback. The tank I bought off ebay had the orig. tube set up to the filler neck, it also had a small vent tube like your pic . It went straight into the tank and stopped in the center in the top of the tank. Not sure what body or year it was designed for, but the tank fit perfectly, so I took that tube around and back up into the trunk , put a couple of coils up high and back down threw the floor of the trunk and below / don't remember exactly far.
My gas has never splashed out when filling like my brand new 68 form S fastback did , back in 1968 . JFYI
Yours doesn`t quite look like mine does tho , it sounds like ur pulling a vacuum on ur tank, to me, I`d vent it ----------

 

[Fgill]

I suspect this is what maybe happening. nothing is vented, thus the starvation issue as fuel consumption is drawing a vacuum.
PO also replaced the tank that does not have the evap outlets. So, to recap, I have an aftermarket sender with plugged return line, incorrect tank, incorrect cap and plugged vents..lol. oh the fun.

 

[67Dart273]

If you could post some photos might help.........the tank /stuff in the trunk, underneath shot of the tank looking to the rear from in front of the axle, and is the 1/4 line next to the fuel line still there "up to front"?