Fuel cap and tank venting

Hello All, couple of questions. I just got a new tank and sender for My 73 Duster and they are identical to what I pulled off. Q1 is the filler cap vented or not? I would think it is a sealed cap what with emissions of the period. Q2 the tank has 1 nipple and the sender has the 2, 1 for supply 3/8 and a 5/16. for a vent or return. Can I plumb this with a looped hard line off the tank nipple or ?

My 73 OEM filler cap is not vented. My tank does not have any nipples, not sure where you are referring too as far as location of this tank nipple. The sending unit has two ports; one supply line and one vent line to the canister under the hood, where its vented to.
The fuel sending unit is a Non-Linear type on all Mopars in order for the gauge to read properly.

a stock 73 tank is going to have all the vapor recovery stuff in the top front.


i know this isn't the right car line, but the separator is the same

Here's from my catalog.

Here is the deal on "venting." ALL vapor system cars use what is commonly known as a "pressure vacuum" cap, which means it has RELIEFS in there to vent over-pressure, either pressure or vacuum. NO Mopar cap in the cars we talk about here uses a vented cap. Up until vapor control systems, they are vented through a tube connected to the filler pipe in the trunk. All the vapor controlled cars have a 1/4" vent line coming up front which ties in with the carbon can system. THIS IS your tank vent and must not be removed, plugged, etc

Caps are a PITA for these cars, as there are several, and they changed year by hear. Oldmanmopar or someone had a great illustration of the caps over the years..........

..........and here we go.......

Vented or non vented fuel cap?



Below is the cars BEFORE vapor control Evap controls started to happen in some 70 cars in CA, not sure if "all cars" in 71, but 72, later, all cars Federally had evap controls

crewchief said:

My 73 OEM filler cap is not vented. My tank does not have any nipples, not sure where you are referring too as far as location of this tank nipple. The sending unit has two ports; one supply line and one vent line to the canister under the hood, where its vented to.
The fuel sending unit is a Non-Linear type on all Mopars in order for the gauge to read properly.

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The car is a former racer and is gutted as far as emissions. The new tank is the same as the one I pulled. One soldered 1/4 inch nipper on top by the sender . I looked at the cap and it has no vent I can see . The rubber gasket is for **** and dont look like it would seal anyway. Can I just run a line from the tank nippel with a circular bend up above tank level? Kind of like the one in my 68 roadrunner. But that has 2 nippers on the tank. It has to vent some place even with the suspect filler cap. Think I will give it a shot and see what happens. When I get it on the road summer time heat will be the acid test. Will report back then .

In that case i would be tempted to duplicate the 69/ earlier vent tube. Braze a tube high into the filler neck, run it up high against the top of the quarter panel, and "U" down and through the floor below.

67Dart273 said:

In that case i would be tempted to duplicate the 69/ earlier vent tube. Braze a tube high into the filler neck, run it up high against the top of the quarter panel, and "U" down and through the floor below.

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Sounds like a good idea. Not a big deal since the filler neck is easy to get out being just installed and lubed up. I will just hard line as much as possible.