Non EEC fuel tank vent

[ASPEC]

Hello,
Does anyone have a pic or diagram of the fuel tank vent hose/breather for a 1974 non eec 454?
The PO had capped both tank's fuel sender vents and that is a big no-no. To make matters worse they installed the wrong filler necks (79-84 instead of 73-74) and the caps are not vented either.
I checked the service manuals but didn't find anything. I am assuming it is similar to a differential vent but would like to know how they were run and if there is anything special about the vent type.
Thanks in advance.

 

[75gmck25]

My ‘75 has three port sending units, and both sides go to a T fitting. That fitting connects to a metal line that runs up to the engine compartment.
At the engine compartment it connects to the vapor canister, and that originally vented into a dedicated port on the carburetor.

In the engine compartment I now have just a vent line from the canister to an open fitting I put on the base of the air cleaner, since my newer Quadrajet does not have the right ports for the canister vent. It probably doesn’t pull much vacuum, but seems to be enough to clear the canister of any vapor.

 

[ASPEC]

My ‘75 has three port sending units, and both sides go to a T fitting. That fitting connects to a metal line that runs up to the engine compartment.
At the engine compartment it connects to the vapor canister, and that originally vented into a dedicated port on the carburetor.

In the engine compartment I now have just a vent line from the canister to an open fitting I put on the base of the air cleaner, since my newer Quadrajet does not have the right ports for the canister vent. It probably doesn’t pull much vacuum, but seems to be enough to clear the canister of any vapor.

I appreciate the response but this '74 2500 came from the factory with NO emissions systems. No evap, No cats, No air pump, etc...
So it won't be the same as any model with an evap cannister.

 

[ASPEC]

Bumpsky...

 

[eric8]

Did you get this sorted out? If your truck had no emissions, I would think the fuel tank sending unit would only have one port (going out to feed fuel to the pump), with all venting taking place through a vented fuel cap.

 

[ASPEC]

Did you get this sorted out? If your truck had no emissions, I would think the fuel tank sending unit would only have one port (going out to feed fuel to the pump), with all venting taking place through a vented fuel cap.

I am just going to route the vent lines under the bed to a spot that makes sense to secure them to.

It must have something to do with the camper special options and the fact it is a Federal emissions not California. This was the last model year for new "leaded fuel" trucks, in 1975 they went to "unleaded fuel only" badges.

Also you would not want "open to atmosphere" fuel caps because on cornering fuel runs up the filler neck. The vent on the sender is centered on top of the tank so fuel will climb up either side of the tank during cornering, leaving the short vent tube in the empty air at the top off the tank.