Fuel vaporization fix

[75dogdart]

First time poster here. I just bought this Dart a month ago, and it was my first experience with old American cars. I've fixed a lot of small things with the help of the search button on this site, but I'm running into a problem and I can't find what I need without posting. This is a 1975 dart, with a 360, and I've got a fuel boiling problem. I started with an electric fuel pump install, this helped but didn't completely solve the issue. Which is, whenever I'm stopped in traffic or make a quick stop at the store, and fuel is sitting in the lines, not moving, I'll take off again and I get a massive stumbling problem. Before the electric pump, the fuel filter would be essentially empty all the time when it was hot, now it is filled up a bit more, but I still have stumbling issues when I park for a few minutes then go back and drive. I think the electric fuel pump helps keep it under pressure so it doesn't vaporize in traffic, but obviously can't do that when I'm parked. So now I'm looking into adding one of the wix filters with a third outlet to lead back to the tank, so the vapors can escape if and when they build up. My charcoal canister is long gone and I have an open port up in the engine bay. I feel like I've read conflicting reports if I can use this as a return. Can I just plumb that third nipple of the filter back into the line that used to go to the charcoal canister and add a vented gas cap? I don't see why not, as long as I can find a gas cap that vents under pressure and vacuum, does one exist? I also don't know what kind of fuel sender I have in the tank, because one port is completely blocked off and I'm not sure what it was originally for? I could use rubber line to connect the blocked port to the hardline that goes up front, and use some rubber line to direct the "original" vent to atmosphere. Or vice-versa, or use a vented cap if I can find one. I'd appreciate any advice, this ain't a race car or a show car, I just want to drive my dodge with the dog and not have annoying stumbling problems. Thanks yall! I added some pics of my fuel sender, the fuel pump install that is running through a relay box and fuses, which is all running through a circuit breaker, and a pic of the dog that just wants to go to the park.

 

[Bewy]

You need a phenolic spacer under the carb. That will reduce heat getting to the carb which will in turn reduce the amount of evaporation. You do not need any other vent lines. The carb has atmospheric events for each float bowl which allows the fumes to go the atmosphere via the air filter.

 

[440 Mike]

Think about routing some steel line and the fuel filter behind the alternator and over the intake manifold. Right now it's over the header.

 

[75dogdart]

Think about routing some steel line and the fuel filter behind the alternator and over the intake manifold. Right now it's over the header.

I was looking at that. The stock line goes right along the frame rail, next to the header. Now that I don't have the mechanical pump, I can route the lines however I want. I did wrap the bottom of the header with a heat wrap and put a sleeve over that part of the fuel line. Just to see if it fixed it, but it didn't. So I'm not opposed to doing some rerouting of lines if it will help.

 

[75dogdart]

You need a phenolic spacer under the carb. That will reduce heat getting to the carb which will in turn reduce the amount of evaporation. You do not need any other vent lines. The carb has atmospheric events for each float bowl which allows the fumes to go the atmosphere via the air filter.

I've seen those recommended. Which is worth looking into. With the mechanical pump, I figured it was cavitating due to vapor. But with the electric, it should push the vapor into the carb and vent it out until it gets enough fuel to shut off the bowls, right? I would think that would happen fast enough that I wouldn't experience any drivability problems. So maybe it is just boiling in the carb itself?

 

[67Dart273]

First, the fuel cap should be a "pressure / vaccum" cap which does NOT mean that it is operationally vented for the engine. This means that if the tank develops excessive internal positive or vacuum pressure, the cap will RELIEVE.

The operational vent is done by the evap emission system, part of which is in the tank (this changes over the years 70-later) and the 1/4" tube which comes to the engine bay. THAT tube is not only part of the evap control system, and originally ties in with the engine bay "carbon can" stuff, but ALSO IS THE operational vent, allowing the tank to properly vent during driving

If you don't need nor want the evap controls, that 1/4 line MUST be up high in the engine bay--to prevent siphoning, and must be left open. You can plumb it into the open air side of the PCV AKA the vent line to the filter bonnet.

If you don't want to do that, figure a safe way to install a fitting up high in the filler neck and convert the vent to a 69/ earlier vehicle. Those used a completely sealed cap

I WOULD NOT RUN a vented cap because of the danger of dribbling fuel over the side when full, etc.

Below is the 69/ earlier style vent. Simple. BE CAREFUL when choosing/ replacing a cap. The caps changed almost every year. There is a "famous" photo posted on here by Steve, OldManMopar, that shows several caps from 70--to the end. They are DIFFERENT

Fuel tank vent

Anyone using a return style fuel system with an OE tank? I’m looking for ideas that are safe and clean.

www.forabodiesonly.com

The secret of the simple old style vent is that the bend goes up high against the top of the quarter panel, and "breaks" any siphon. It simply goes down alongside the filler tube and punches through the floor gasket, and open ends INSIDE the rear frame rail. I guess this was to protect it from road mud, etc. Any fuel will simply dribble out the bottom of the frame rail

 

[65TerrorCuda]

 

[75dogdart]

First, the fuel cap should be a "pressure / vaccum" cap which does NOT mean that it is operationally vented for the engine. This means that if the tank develops excessive internal positive or vacuum pressure, the cap will RELIEVE.

The operational vent is done by the evap emission system, part of which is in the tank (this changes over the years 70-later) and the 1/4" tube which comes to the engine bay. THAT tube is not only part of the evap control system, and originally ties in with the engine bay "carbon can" stuff, but ALSO IS THE operational vent, allowing the tank to properly vent during driving

If you don't need nor want the evap controls, that 1/4 line MUST be up high in the engine bay--to prevent siphoning, and must be left open. You can plumb it into the open air side of the PCV AKA the vent line to the filter bonnet.

If you don't want to do that, figure a safe way to install a fitting up high in the filler neck and convert the vent to a 69/ earlier vehicle. Those used a completely sealed cap

I WOULD NOT RUN a vented cap because of the danger of dribbling fuel over the side when full, etc.

Below is the 69/ earlier style vent. Simple. BE CAREFUL when choosing/ replacing a cap. The caps changed almost every year. There is a "famous" photo posted on here by Steve, OldManMopar, that shows several caps from 70--to the end. They are DIFFERENT

http://[URL][URL]https://www.forabodiesonly.com/mopar/threads/fuel-tank-vent.505304/

[/URL][/URL]

The secret of the simple old style vent is that the bend goes up high against the top of the quarter panel, and "breaks" any siphon. It simply goes down alongside the filler tube and punches through the floor gasket, and open ends INSIDE the rear frame rail. I guess this was to protect it from road mud, etc. Any fuel will simply dribble out the bottom of the frame rail

I appreciate this info. So if I add the older vent style to my filler tube, can I then use the existing vent tube as my fuel/vapor return line? I also have that blocked off port on my sending unit, which after some googling, looks like it is a return port. Using the existing 1/4 inch line would just be convenient, but I could attempt to bend up a new line and keep the current venting arrangement.

 

[75dogdart]

View attachment 1716380973

I'll take a better look at this. I did glance over it while I was under there, and the clamp is higher up on the hose than the picture suggests, and the gap is where the tube starts to make it's bend. The clamp was tight, and since I only had issues when it was hot, I figured it was not the issue. But I'll get back under there and re-evaluate.

 

[George Jets]

Here is the proper way (factory) to run your fuel line and steel fuel filter. Down low away from the heat, fuel filter pointing up > so air bubble goes up and out.

You have your rubber line and plastic fuel filter going over the hot headers.

Those headers are like hot water radiators in the old homes kicking out a lot of heat. Cast manifolds send the heat out of the engine bay out to the back of the car.



* * * * *

 

[George Jets]

Think about it, headers are kicking out 400 + degrees heat, the intake manifold runs at 160 degrees. Big difference there on which one is going to boil the fuel.


* * * * *

 

[75dogdart]

Think about it, headers are kicking out 400 + degrees heat, the intake manifold runs at 160 degrees. Big difference there on which one is going to boil the fuel.


* * * * *

I'll reroute it, however I will say the rubber line is much further away from the header than the hardline. The hardline currently jogs over into the engine bay along the inside of the frame rail and runs right next to the header collector on its way to the factory fuel pump location. This routing looks factory, but the guy I bought it from said he thinks the car was a 6 cylinder originally. I've tried to find factory fuel routing diagrams and it looks like all of the cars had it routed the same way. But maybe not, maybe the 8 cylinder cars had it routed further away. I'd like to reroute all the lines further away from the heat. I'm at work now so I can't get a picture of it at the moment, but it essentially does this

 

[MDchanic]

Okay, I'll be the contrary SOB here.

... whenever I'm stopped in traffic or make a quick stop at the store... I'll take off again and I get a massive stumbling problem.

... I've got a fuel boiling problem...

... I think the electric fuel pump helps keep it under pressure so it doesn't vaporize...

How do you know this? Have you seen or heard boiling fuel? Have you measured the pressure? Do you know the boiling point of gasoline? Have you measured its temperature?

... I started with an electric fuel pump... this helped but didn't completely solve the issue.

Did it really help, or did it just seem to because you put a bunch or time and money into it?

... Before the electric pump, the fuel filter would be essentially empty all the time when it was hot, now it is filled up a bit more...

This is the normal condition. An inline fuel filter will not fill up. It will contain air.
Again, this is completely normal. You are fixing something that it not a problem.
This is why the best choice is a metal filter: You can't see the air inside and get upset.
That and the whole "Not breaking and spraying fuel all over your engine" thing.

... Can I just plumb that third nipple of the filter back into the line that used to go to the charcoal canister and add a vented gas cap?

Do you have a factory service manual for your car? If not, you need to get one. It will show all of the lines and connections that the factory put there, which will include evaporative emissions equipment that is no longer there. From there, you can figure out which lines go where and connect them as appropriate for your needs.

... I also don't know what kind of fuel sender I have in the tank, because one port is completely blocked off and I'm not sure what it was originally for?

Factory service manual.


My recommendations, in no particular order:

• As others have said, there are a lot of variations on gas caps through the '70s. Only one type will fit. Whichever type that is is the one you need.
• The original system vented the tank in a complex way. It's gone now. You need to have the tank vented somehow, in a safe manner, as 67Dart273 described above.
• All cars benefit from a return-circulating fuel pump system. As far as I know, yours had one when it was made (others, please tell me if I'm wrong). The correct mechanical fuel pump, with a recirculation nipple, connected to the original recirculation line, connected to the original recirculation nipple on the sender, will do the job, and you won't need a mechanical fuel pump, or a fancy fuel filter.

And now for my actual point:

... whenever I'm stopped in traffic or make a quick stop at the store... I'll take off again and I get a massive stumbling problem.

You have "stumbling" after stopping and turning off the engine while warm.

You have decided (without evidence) that the problem is "boiling" fuel, and have taken a number of steps to fix that, and they haven't helped.

Your problem may be fuel that is boiling so tenaciously (but only while stopped) that it is resisting your efforts, or you may have a different problem.

An electrical fuel pump, "pushing" from the tank, will solve darned near any vapor-lock or "boiling fuel" problem. If, in fact, you have no liquid fuel whatsoever in your fuel lines or your float bowl, whether you have fuel vapor or air, the electrical pump will push fuel through and fill the float bowl in a second or two. In this case, all you would need to do would be to turn on the key, wait a second or two for the sound of the pump to change, indicating that it has built up pressure, and start the car, and it would drive normally.

Also, an electrical fuel pump, not connected through the oil pressure sensor or some similar means of automatic disconnect, will continue to pump out your whole tank in the event of a crash, just so you know. I've hooked them up without a safety, we've all done it, but you've only been doing this for a month, so it bears mentioning.

If you would describe your problem in more detail, that would help us to help you.
"Stumbling" is not very descriptive.

Personally, I suspect that your carburetor is "loading up" (ie: a "too much fuel" problem), and that you need to start it with the pedal floored and "blow it out" before proceeding.
This should not represent "normal operation," but is how one deals with this problem in the short term.
Have you rebuilt your carburetor? Set the float level? Is the float sinking? Is the needle and seat leaking?
These are all of the questions I would ask.

My final recommendation:
Go get a "Zip Kit" for your carburetor, as well as a float and a gallon or two of evil carburetor-soak cleaner, take the carb off, read the factory manual, take it apart, clean it, rebuild it (you'll also need a source of compressed air to blow it out while cleaning it), reinstall it, adjust it, and see how it works.

Good luck!

– Eric

 

[75dogdart]

Okay, I'll be the contrary SOB here.






How do you know this? Have you seen or heard boiling fuel? Have you measured the pressure? Do you know the boiling point of gasoline? Have you measured its temperature?



Did it really help, or did it just seem to because you put a bunch or time and money into it?



This is the normal condition. An inline fuel filter will not fill up. It will contain air.
Again, this is completely normal. You are fixing something that it not a problem.
This is why the best choice is a metal filter: You can't see the air inside and get upset.
That and the whole "Not breaking and spraying fuel all over your engine" thing.



Do you have a factory service manual for your car? If not, you need to get one. It will show all of the lines and connections that the factory put there, which will include evaporative emissions equipment that is no longer there. From there, you can figure out which lines go where and connect them as appropriate for your needs.



Factory service manual.


My recommendations, in no particular order:

• As others have said, there are a lot of variations on gas caps through the '70s. Only one type will fit. Whichever type that is is the one you need.
• The original system vented the tank in a complex way. It's gone now. You need to have the tank vented somehow, in a safe manner, as 67Dart273 described above.
• All cars benefit from a return-circulating fuel pump system. As far as I know, yours had one when it was made (others, please tell me if I'm wrong). The correct mechanical fuel pump, with a recirculation nipple, connected to the original recirculation line, connected to the original recirculation nipple on the sender, will do the job, and you won't need a mechanical fuel pump, or a fancy fuel filter.

And now for my actual point:

You have "stumbling" after stopping and turning off the engine while warm.

You have decided (without evidence) that the problem is "boiling" fuel, and have taken a number of steps to fix that, and they haven't helped.

Your problem may be fuel that is boiling so tenaciously (but only while stopped) that it is resisting your efforts, or you may have a different problem.

An electrical fuel pump, "pushing" from the tank, will solve darned near any vapor-lock or "boiling fuel" problem. If, in fact, you have no liquid fuel whatsoever in your fuel lines or your float bowl, whether you have fuel vapor or air, the electrical pump will push fuel through and fill the float bowl in a second or two. In this case, all you would need to do would be to turn on the key, wait a second or two for the sound of the pump to change, indicating that it has built up pressure, and start the car, and it would drive normally.

Also, an electrical fuel pump, not connected through the oil pressure sensor or some similar means of automatic disconnect, will continue to pump out your whole tank in the event of a crash, just so you know. I've hooked them up without a safety, we've all done it, but you've only been doing this for a month, so it bears mentioning.

If you would describe your problem in more detail, that would help us to help you.
"Stumbling" is not very descriptive.

Personally, I suspect that your carburetor is "loading up" (ie: a "too much fuel" problem), and that you need to start it with the pedal floored and "blow it out" before proceeding.
This should not represent "normal operation," but is how one deals with this problem in the short term.
Have you rebuilt your carburetor? Set the float level? Is the float sinking? Is the needle and seat leaking?
These are all of the questions I would ask.

My final recommendation:
Go get a "Zip Kit" for your carburetor, as well as a float and a gallon or two of evil carburetor-soak cleaner, take the carb off, read the factory manual, take it apart, clean it, rebuild it (you'll also need a source of compressed air to blow it out while cleaning it), reinstall it, adjust it, and see how it works.

Good luck!

– Eric

Appreciate the advice. When I say it helped, the stumbling/dying, falling on its face, not taking throttle of any kind, however you want to describe it, no longer happens when the car has been stopped at a light or idling around in slow traffic. It does still happen when I park, shut it off for a few minutes, then go drive again. It happens a minute or two after getting out of the parking lot and I get on the gas a bit. I left off, it clears up, and drives fine. I'm aware a fuel filter doesn't need to always be full, but do you agree this empty (first pic) is a problem? This was with the mechanical pump, and after it cooled down slightly with the hood open and running. It would start pumping tons of bubbling fuel into it then the bubbles would clear out.

 

[Demonracer]

Have you checked the sock on the fuel line in the tank, is the tank full of rust and other crap?

 

[67Dart273]

I appreciate this info. So if I add the older vent style to my filler tube, can I then use the existing vent tube as my fuel/vapor return line? I also have that blocked off port on my sending unit, which after some googling, looks like it is a return port. Using the existing 1/4 inch line would just be convenient, but I could attempt to bend up a new line and keep the current venting arrangement.

View attachment 1716381016

I would use the sender port for a return. By the way this is simple to do. Wix and others make filters with built in return ports

Here is 5/16, with 1/4" return. They must be either vertical or horizontal, with the return port "up"

https://www.oreillyauto.com/detail/c/wix/wix-fuel-filter/wix0/33040

 

[MDchanic]

When I say it helped, the stumbling/dying, falling on its face, not taking throttle of any kind, however you want to describe it, no longer happens when the car has been stopped at a light or idling around in slow traffic.
It does still happen when I park, shut it off for a few minutes, then go drive again.

Are you sure your choke is opening all the way?

It happens a minute or two after getting out of the parking lot and I get on the gas a bit.

I left off, it clears up, and drives fine.

That timing is not what I would expect, whether from a vapor-lock or "boiling fuel" perspective, or a from a fuel-starvation aspect.

Vapor-lock should make it hard, or impossible, to start, but once it gets going, it should be fine. 2 minutes after getting started really doesn't fit here.

Fuel starvation that shows up 2 minutes into driving would also be expected to affect any or every higher-throttle situation, such as passing, driving uphill, etc.
If you had air or fuel vapor or whatever in the lines initially, it should be 100% gone after 2 minutes.

Which brings up my favorite diagnosis adage:
"All fuel problems are actually electrical.
All electrical problems are actually the fuel system."

If you can establish with certainty that you are getting neither too much nor too little fuel, then look at your ignition system. I think you said it was electronic, didn't you?
But first, I'd take a good look at the carburetor.

I'm aware a fuel filter doesn't need to always be full, but do you agree this empty (first pic) is a problem?

View attachment 1716381100

No that looks fine to me.

For an experiment, you can reorient it so that the fuel comes in at the top and exits at the bottom. The car will run, and there will always be a little fuel at the bottom, but it won't fill up.

This was with the mechanical pump, and after it cooled down slightly with the hood open and running. It would start pumping tons of bubbling fuel into it then the bubbles would clear out.

It shouldn't be pumping air. If you have a pinhole (or three) in your fuel lines, or an equivalent leak in any of your other fuel connections, on the suction side, it can break the vacuum, your pump will suck air, and you will have all sorts of running and starting problems.
(If the hole is on the pressure side, you will have leaks).

Did the electric pump, closer to the gas tank, help this problem?


I look at it this way:

Too little fuel will cause fuel starvation and will usually be worse the more power you try to get. The one exception to this is a suction-side pinhole, which will often break the suction enough to cause hard starting (lots of cranking to first get fuel up to the carburetor), but once it has gotten fuel up, the hole will not prevent fuel from flowing, and it will run fairly well.

Other things that cause fuel starvation include any kind of restriction, such as a gummed-up pickup sock, a pinched line, dirt in the line, broken-down hose rubber in the line, or a piece of crud in the needle seat, as well as things that reduce pump function, such as a hole in a diaphragm or a leaky valve.

Too much fuel will cause rich running and loading up. When serious it will cause black smoke.
Things that cause too much fuel, aside from blatant things like wrong carburetor or wrong jetting, are a leaky needle and seat (ALSO sometimes caused by a piece of crud between the needle and seat, or, usually, by wear), a misadjusted float, a "heavy" float (saturated or filled with fuel), or a choke that doesn't open all the way.

If your fuel level is slightly high, or your choke is a bit closed, you may experience the same symptoms you are having now, where it starts rich, but once the excess fuel is cleared, it will run passably, but not as well as it would if all was well, and usually with poor fuel economy.

You DO have a factory manual, right?

If not, you NEED to get one. It's two volumes.
There's one here. $30 with $10 shipping. Buy it now.

– Eric

 

[AJ/FormS]

Okay, I'll be the contrary SOB here.






How do you know this? Have you seen or heard boiling fuel? Have you measured the pressure? Do you know the boiling point of gasoline? Have you measured its temperature?



Did it really help, or did it just seem to because you put a bunch or time and money into it?



This is the normal condition. An inline fuel filter will not fill up. It will contain air.
Again, this is completely normal. You are fixing something that it not a problem.
This is why the best choice is a metal filter: You can't see the air inside and get upset.
That and the whole "Not breaking and spraying fuel all over your engine" thing.



Do you have a factory service manual for your car? If not, you need to get one. It will show all of the lines and connections that the factory put there, which will include evaporative emissions equipment that is no longer there. From there, you can figure out which lines go where and connect them as appropriate for your needs.



Factory service manual.


My recommendations, in no particular order:

• As others have said, there are a lot of variations on gas caps through the '70s. Only one type will fit. Whichever type that is is the one you need.
• The original system vented the tank in a complex way. It's gone now. You need to have the tank vented somehow, in a safe manner, as 67Dart273 described above.
• All cars benefit from a return-circulating fuel pump system. As far as I know, yours had one when it was made (others, please tell me if I'm wrong). The correct mechanical fuel pump, with a recirculation nipple, connected to the original recirculation line, connected to the original recirculation nipple on the sender, will do the job, and you won't need a mechanical fuel pump, or a fancy fuel filter.

And now for my actual point:

You have "stumbling" after stopping and turning off the engine while warm.

You have decided (without evidence) that the problem is "boiling" fuel, and have taken a number of steps to fix that, and they haven't helped.

Your problem may be fuel that is boiling so tenaciously (but only while stopped) that it is resisting your efforts, or you may have a different problem.

An electrical fuel pump, "pushing" from the tank, will solve darned near any vapor-lock or "boiling fuel" problem. If, in fact, you have no liquid fuel whatsoever in your fuel lines or your float bowl, whether you have fuel vapor or air, the electrical pump will push fuel through and fill the float bowl in a second or two. In this case, all you would need to do would be to turn on the key, wait a second or two for the sound of the pump to change, indicating that it has built up pressure, and start the car, and it would drive normally.

Also, an electrical fuel pump, not connected through the oil pressure sensor or some similar means of automatic disconnect, will continue to pump out your whole tank in the event of a crash, just so you know. I've hooked them up without a safety, we've all done it, but you've only been doing this for a month, so it bears mentioning.

If you would describe your problem in more detail, that would help us to help you.
"Stumbling" is not very descriptive.

Personally, I suspect that your carburetor is "loading up" (ie: a "too much fuel" problem), and that you need to start it with the pedal floored and "blow it out" before proceeding.
This should not represent "normal operation," but is how one deals with this problem in the short term.
Have you rebuilt your carburetor? Set the float level? Is the float sinking? Is the needle and seat leaking?
These are all of the questions I would ask.

My final recommendation:
Go get a "Zip Kit" for your carburetor, as well as a float and a gallon or two of evil carburetor-soak cleaner, take the carb off, read the factory manual, take it apart, clean it, rebuild it (you'll also need a source of compressed air to blow it out while cleaning it), reinstall it, adjust it, and see how it works.

Good luck!

– Eric

well said, well organized.

 

[AJ/FormS]

And finally,
What are the chances that your transfer slots are too far closed, usually cuz the ignition timing is too far advanced.

 

[volaredon]

While I generally like them, I've only ever had that problem with AFB/Edelbrock carbs. Don't know why that is. Other than that I actually like those carbs. The one I put on my diplomat was the worst for it and yeah I could hear the gas boil. And yeah I did do away with the 3 cats which I would have thought would have cut down tremendously on the heat bottled up in the engine compartment being that 2 of them were directly off the manifolds.
I have a couple of TQs around to use on my 78 fury and my truck project just to get around that problem.

 

[SixPaksRule]

Please check the under the hood after driving temperatures at the thermostat outlet and base of carb. What's the temps?

The fuel lines you have configured are not safe and a bit of a caveman type configuration. The steel factory lines were configured that way for a good reason

 

[75dogdart]

Update: All fixed. Thank you to those who answered my original question regarding the vent tube and gas cap. I used the wix filter as planned, but ran a new return line. That took care of my vapor problem as expected.

 

[MDchanic]

Thank you for the update.

It's always good to find out how things turned out, and whether our own personal theories were correct.
Or not.

- Eric