Vented or non vented fuel cap?

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craigb

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I recently left my fuel cap at a gas station and need to replace it on my 71 Dart. Mega Parts lists non vented cap for 1971 and up and a vented cap for up to 71. How do I determine if I need vented or non vented cap for 71 A body?
 
There is a large tube in the trunk that is separate from fill pipe that I assume has something to do with vapor recovery or venting the tank.
 
up through 69 and "some of" 70 all these used UNvented caps. The venting was via a vent tube welded into the filler neck, goes up against the top of the quarter, then down through the trunk floor and "dead ends" open ended inside the rear frame rail. Once again, that was earlier

Like so

2cmugso.jpg


In CA in part of 70, and all later, the evap vapor control junk came about, IE "the carbon can." This system CHANGED nearly every single year or two in some ways or other

"OldmanMopar" I believe showed the differences in caps. This is determined by your FILLER NECK. These are NOT vented. They are known as "pressure vacuum"

72blunblu it turns out............

http://www.forabodiesonly.com/mopar/showpost.php?p=1969928450&postcount=6

attachment.php


The venting in those with the "pressure vacuum" caps is done by means of the evap vapor control system.
 
Figured it out with help of Year One, changed from old style to newer style in June of 71. Our car was built in December of 70 so I got the older style.
 
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