Fuel Tank Vent Line Clogged or Blocked off?
- Thread starter TF360
- Start date
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If it's really a vented cap, probably nothing. But if the cap is not vented, or is malfunctioning and the tank is pulling a vacuum because the vent is stopped up, then maybe. Remove the cap when it starts runnin funny and see if it clears up. If it has a vent to begin with, it probably shouldn't have a vented cap.
NONE of the caps are operationally vented. The EVAP caps are what is called "pressure vacuum" and are supposed to relieve excess pressure, both vacuum and pressure. They are NOT meant for venting the tank.
The line from the tank system up to the engine bay IS THE OPERATIONAL tank vent and is/ was also part of the "carbon can" EVAP system.
DO YOU HAVE a factory shop manual? NO you can not download it free from MyMopar. I have one and will be glad to mail it to you if you contact me. It will cost you a couple dollars in shipping.
The 1/4" line up front MUST be kept open and high in the engine bay. Some guys plumb them into the air cleaner bonnet part of the crancase vent system.
I have advocated MANY times for guys to consider modifying their filler neck to imitate the simple 69/earlier vent system, which is simply a 1/4" tube out of the filler neck, goes up and upside down "U" at the top of the quarter panel, then tube goes over and runs / anchored along the filler tube and pokes through the grommet in the trunk floor. OEM, they simply ended inside the rear frame rail. I would guess that was to help keep bugs, mud dawbers, and road splash out of the vent tube end.
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The line from the tank system up to the engine bay IS THE OPERATIONAL tank vent and is/ was also part of the "carbon can" EVAP system.
DO YOU HAVE a factory shop manual? NO you can not download it free from MyMopar. I have one and will be glad to mail it to you if you contact me. It will cost you a couple dollars in shipping.
The 1/4" line up front MUST be kept open and high in the engine bay. Some guys plumb them into the air cleaner bonnet part of the crancase vent system.
I have advocated MANY times for guys to consider modifying their filler neck to imitate the simple 69/earlier vent system, which is simply a 1/4" tube out of the filler neck, goes up and upside down "U" at the top of the quarter panel, then tube goes over and runs / anchored along the filler tube and pokes through the grommet in the trunk floor. OEM, they simply ended inside the rear frame rail. I would guess that was to help keep bugs, mud dawbers, and road splash out of the vent tube end.
Fuel tank vent
Anyone using a return style fuel system with an OE tank? I’m looking for ideas that are safe and clean.
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Yes, Townsend it is vented
Check the lines to the charcoal canister.
Read this thread from March 4 2025 for a more detailed explanation.
1973 and 1974 evap systems are identical.
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1973 and 1974 evap systems are identical.
Gas Tank Vacuum
Went to go riding around Saturday. Started my '73 Duster 340, it ran about a minute and run out of gas. I know there was about a quarter tank, but the gas gauge doesn't work right so I went and got some gas. When I took the gas cap off, there was a vacuum. Once the gas got to the carburetor...
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THE ORIGINAL CAP ON A 74 IS NOT VENTED. Read post 6. They are "pressure vacuum" relief caps
As I said earlier, there is only ONE vent out of the tank and that is in fact, the 1/4" line going to the front. NOTICE the "overfill valve" up near the front of that tube. That valve must be working or removed.
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Good picture Dell.
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