Vapor return or liquid return line?

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SomeRandomDude

SomeRandomDude

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I occasionally fight hard starts on my 73 Dart Swinger which seems to be a heat soak issue. After reading a few threads online about adding a vapor return line and filter I crawled under the car and found what I assume to be a vapor return line running along side the fuel line - though it doesn't connect to the sender at the tank - but several inches above it closer to the top of the tank (see picture). That line runs to the engine bay with the fuel line but then stops short half way through the engine bay. I bought a vapor returned style filter and hooked everything up including that line and when I cranked it over discovered that there was a crack halfway down that line once fuel started flowing out of it. So now I need to replace that line - but I thought it would only be fuel vapor in there? Why was there liquid fuel or is this actually a liquid return line?
1000001398.jpg
 
I think that's the tank vent and should terminate at the charcoal canister under the hood. I don't believe these vehicles have a provision for a return line. Use an aftermarket sender, or fabricate one yourself. Lets see what the consensus is?
 
Go over to Mymopar.com and download the 1973 dodge service manual. It will tell you all about it. That way you can get it from the horse's mouth. It's a free download.
 
The fuel "vapor" filters have a small bleed hole so vapor can escape but if there is no vapor a small amount of fuel will be escape there.

If you can find a ethanol free gas supplier near you, run your tank down to as close to empty as you feel safe and then fill full with ethanol free, and see if your issue goes away with all the lines and filter as it was before the filter change.

Pure-gas.org
 
Dana67Dart said:
The fuel "vapor" filters have a small bleed hole so vapor can escape but if there is no vapor a small amount of fuel will be escape there.

If you can find a ethanol free gas supplier near you, run your tank down to as close to empty as you feel safe and then fill full with ethanol free, and see if your issue goes away with all the lines and filter as it was before the filter change.

Pure-gas.org
Click to expand...
@RustyRatRod pointed me in the direction of the factory repair manual (insanely better than the Hayes I have by the way...) it appears that second line is the vent that used to run to a charcoal canister which has since been deleted. I'll try your idea about the ethanol free route but I'd still like to figure a way for adding a vapor return line as a fail safe. Would I just look for a sending unit with a return line built in?
 
SomeRandomDude said:
@RustyRatRod pointed me in the direction of the factory repair manual (insanely better than the Hayes I have by the way...) it appears that second line is the vent that used to run to a charcoal canister which has since been deleted. I'll try your idea about the ethanol free route but I'd still like to figure a way for adding a vapor return line as a fail safe. Would I just look for a sending unit with a return line built in?
Click to expand...
You could simply find a charcoal canister and reinstall it. They are actually a good thing to have. All kinda benefits, not the least of which can pick up a little MPG.
 
Couple of things probably in play here.
First, fix that line.
Now for the fuel or vapor question. From the FSM:
1725760701381.png

Note that it says it is designed to "allow fuel vapors to return to the fuel tank", so there's part of your answer.
The rest of the answer involves the parts being used. The fuel filter does not simply have an additional outlet, it has a .060 orifice to bleed off the vapors. Or more accurately, it is supposed to. Many filters in recent years don't have the restrictor orifice, either due to cost cutting, bad quality control, whatever. I have personally run into this with both Wix and Fram filters, but it seems to be hit and miss. When the restrictor/orifice is not present, the third line becomes a "wet" return since there is nothing to restrict fuel flow. This also means that it bleeds off fuel pressure and flow, potentially causing fuel feed issues.
The remedy? Make sure your filter has the .060 orifice in the filter's return tube. It is plainly visible if you look in there (but I can't photograph it well, otherwise I would include pictures of filters with and without the restrictors- same manufacturers and part numbers!), and if it's missing you can see the paper filter media.
The other option is to add your own restrictor- I make mine out of a 1/4" brass hose connector barb, and tap the inside for a 1/4-20 thread, and screw in a brass allen screw that has been drilled to .060- looks just like a carb jet. That way I don't have to worry if my replacement filter has the correct restrictor or not. Works slick.
Plumb the line to the 1/4" fitting near the top of the tank- no worries there, and no need for a different aftermarket (and notoriously inaccurate) sending unit.
 
Professor Fate said:
Couple of things probably in play here.
First, fix that line.
Now for the fuel or vapor question. From the FSM:
View attachment 1716300474
Note that it says it is designed to "allow fuel vapors to return to the fuel tank", so there's part of your answer.
The rest of the answer involves the parts being used. The fuel filter does not simply have an additional outlet, it has a .060 orifice to bleed off the vapors. Or more accurately, it is supposed to. Many filters in recent years don't have the restrictor orifice, either due to cost cutting, bad quality control, whatever. I have personally run into this with both Wix and Fram filters, but it seems to be hit and miss. When the restrictor/orifice is not present, the third line becomes a "wet" return since there is nothing to restrict fuel flow. This also means that it bleeds off fuel pressure and flow, potentially causing fuel feed issues.
The remedy? Make sure your filter has the .060 orifice in the filter's return tube. It is plainly visible if you look in there (but I can't photograph it well, otherwise I would include pictures of filters with and without the restrictors- same manufacturers and part numbers!), and if it's missing you can see the paper filter media.
The other option is to add your own restrictor- I make mine out of a 1/4" brass hose connector barb, and tap the inside for a 1/4-20 thread, and screw in a brass allen screw that has been drilled to .060- looks just like a carb jet. That way I don't have to worry if my replacement filter has the correct restrictor or not. Works slick.
Plumb the line to the 1/4" fitting near the top of the tank- no worries there, and no need for a different aftermarket (and notoriously inaccurate) sending unit.
Click to expand...
Thanks for this reply - I really like your idea on that restrictor. To clarify - are you saying you plumb in a bung for a new return at the top of the tank or do you use the one we've now figured out is the vent. Doesn't the tank still need a vent?
 
Use the tube at the top for your return. It originally was a vent via the charcoal cannister, it doesn't work well as an atmospheric vent since it is in the main body of the tank and can be below fuel level when the tank is full; so use it as the return. From your original post I'm assuming (maybe I shouldn't...) that the emissions and evap systems have been axed. If that is the case, you will need to vent the tank another way- either by adding an early-style vent tube to the filler neck as suggested by others above, or by using a vented filler cap. *I believe* that a Chevy (I know, I know...) pickup gas cap from the mid '70s is vented and fits a Mopar filler tube, but due to filler variations over the years I can't say for sure it fits the '73 filler neck. Maybe someone else can confirm this particular combination one way or another. I know the Chevy caps were even being sold by some vendors as a replacement for certain Mopar caps, but I don't recall which years.
1725768070047.png
 
I am against using vented caps. Too big a risk, if the tank is full, and maybe you park with the filler a bit "down" that it will leak down the side of the car. Either convert it to mimmick a 69/ earlier vent, (tube high in the filler tube) or plumb an additional fitting into the tank.
 
67Dart273 said:
I am against using vented caps. Too big a risk, if the tank is full, and maybe you park with the filler a bit "down" that it will leak down the side of the car. Either convert it to mimmick a 69/ earlier vent, (tube high in the filler tube) or plumb an additional fitting into the tank.
Click to expand...
That would be my preferred method also, although it is my understanding that these vented caps are not an "open" vent; but use a check valve to avoid fluid leakage just like a rollover valve does. Just trying to give the OP some options here.
 
Professor Fate said:
Couple of things probably in play here.
First, fix that line.
Now for the fuel or vapor question. From the FSM:
View attachment 1716300474
Note that it says it is designed to "allow fuel vapors to return to the fuel tank", so there's part of your answer.
The rest of the answer involves the parts being used. The fuel filter does not simply have an additional outlet, it has a .060 orifice to bleed off the vapors. Or more accurately, it is supposed to. Many filters in recent years don't have the restrictor orifice, either due to cost cutting, bad quality control, whatever. I have personally run into this with both Wix and Fram filters, but it seems to be hit and miss. When the restrictor/orifice is not present, the third line becomes a "wet" return since there is nothing to restrict fuel flow. This also means that it bleeds off fuel pressure and flow, potentially causing fuel feed issues.
The remedy? Make sure your filter has the .060 orifice in the filter's return tube. It is plainly visible if you look in there (but I can't photograph it well, otherwise I would include pictures of filters with and without the restrictors- same manufacturers and part numbers!), and if it's missing you can see the paper filter media.
The other option is to add your own restrictor- I make mine out of a 1/4" brass hose connector barb, and tap the inside for a 1/4-20 thread, and screw in a brass allen screw that has been drilled to .060- looks just like a carb jet. That way I don't have to worry if my replacement filter has the correct restrictor or not. Works slick.
Plumb the line to the 1/4" fitting near the top of the tank- no worries there, and no need for a different aftermarket (and notoriously inaccurate) sending unit.
Click to expand...
Where does the 1/4 barb with the .060 orifice get installed?
 
Professor Fate said:
Just like S'cuder mentioned- in the 1/4" return hose just off from the filter.
Click to expand...
I dug up a bad picture of how I made mine. Similar to what was mentioned, but I made mine out of a barb fitting, a pipe plug, and a carb jet. I tapped the inside of the barb fitting for the pipe plug, then tapped the pipe plug for the jet. I tested a few different jet sizes to tweak the fuel pressure at the carb. My notes show that a .076" jet gave me 5.5psi and a .028" jet gave me 6.2psi at the carb. No restriction gave me 4.5psi.

Fuel Return 2.JPG

My latest revision is smaller and inline with the return.

IMG_4546.png
 
Last edited:
You don't need to go to that work for an orifice. Wix (and others) make several different configurations of inline fuel filters with a 1/4" return already built in. Once again, do not connect that to the vapor line unless you provide a vent elsewhere. That IS the vent for the tank in your system

Wix 33040 for 5/16 tube and 1/4" return, 33041 for 3/8 tube and 1/4 return


wix-33041.jpg
 
Read this. You don't mention which engine your car has, but read this, too. Make sure you've got the correct thick heat-insulating base gasket between the carb and the intake manifold, and that your manifold heat control valve is intact and working, not stuck.
 
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