How do I stop vapor lock?

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A good insulator gasket under the carb, make sure the exhaust manifold on the passenger side does not have a stuck EFE valve, you can also insulate and check routing of fuel line under the hood to reduce heat transfer to it.
 
TrailBeast said:
Oh believe me, being and Edelbrock owner I know about todays fuel issue's and engine heat.
Shielding/rerouting the fuel lines and running an electric pump helped, that and blocking off crossovers.
I was just commenting on how people think a fuel filter is always going to be full of gas or there is a problem.
One problem I see is that even though a return gets cooler fuel closer to the carb it doesn't replace the hot fuel already in it. (like on a hot startup)
Click to expand...

Another reason I ditched the eddie for EFI. Got tired of the hot start issues, constant cranking after sitting for a few days, inconsistent AFRs...

You're 100% correct though, too many people think air (or vapor, or lack of fuel) in the filter is a problem when it isn't.
 
67Dart273 said:
There IS NO return line. You have to add one, re rework the vent system Read my earlier post. Either you have an old style (69/ earlier) vent up in the filler tube, or you have an evap control system with the line going up to the front. READ THE shop manual

If you don't have the evap system, you will have to add a line to the front

If you DO have the evap system, you will either have to convert the vent to the old 69 style, or else add a second line, because the line up to the front IS the tank vent on the cars with evap controls.

As I said earlier, SEVENTY is the split year. Normally, CA state cars got evap controls, 49 states got the "69 style" vent

The other things you can try is to examine the fuel tube routing up by the engine / exhaust. Maybe someone changed the routing. Maybe you have headers "made it worse". Try building a heat shield / glass insulation.....you can buy Summit, etc

Consider installing a rear mount pump.

IT ALSO might be "other problems" YOU NEED to check it out

Is the tank vent plugged? Try removing the cap

Is the tank pickup sock plugged? Supply hose from tank to tube collapsing, restriction in the supply tube?

BAD fuel pump? Again, the service manual has procedures to check out the pump
Click to expand...


I am crunched for time right now and I gotta make another 300 mile trip. I re-routed the fuel line coming from the pump going to the carb. It had a steel line going between the fuel pump, the water pump, the alternator and was very close to the block too. I figured it was cooking in the steel fuel line going between all that stuff. Now it goes along the fender well and over the alternator to the carb.

I don't have the time to look into all the things you suggested, though I really appreciate the suggestions. I have a vent hose that goes from the sending unit to the upper end of the filler tube. Why that is there I have no idea. But I just replaced the rubber hose that was already on there a long long time ago and remembered when I looked in the trunk.

Maybe that line is hooked up wrong. I do have a Chiltons, but not a real/Chrysler manual.

I will have more time after this trip, I hope, and after this weekend I should have more time to investigate and fix this problem permanently.

Thanks!
 
Phreakish said:
Seen this before and it was related to an improper gas cap. What kind of cap are you running now? OEM? Parts store replacement?
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Locking after market cap. I will look into a new one. It is old.

Thanks
 
Survey says!!!

I need to determine if the fuel pump is malfunctioning. That is easy enough, I will replace it. I also need to look into an electric fuel pump. The third thing is to determine if the bowl vent is opening/working. Like one of ya'll said, I don't have the information or experience with adding a fuel return line. There is a line there I could easily "T" into, but I don't know it that will work. It goes from the sending unit to near the top of the filler tube. Which I don't even know if that is correct. The easiest thing that I can do is try a new cap.

I am in a pinch for time and don't even have time to change out the fuel pump before my trip. But I have to go. Do or die. If the fuel pump quits on me, I can just replace it. I have a spare. If the pressure builds again, I can disconnect the fuel line again and vent the pressure.

In a perfect world, I could investigate and fix the problem with no problem. Problem is I am pinched for time, don't have a lot of money, no Chrysler manuals to go by, and I do not have any really experienced mechanics that know what a Mopar is to ask. So you guys are it. I have to go on this trip. Maybe I can explain more later, but it is imperative that I go. If it dies on the side of the road, I can try to fix it. But I have to go.

Thanks for all your replies. I will let you know how my trip went when I get back...
 
fuel line- I have found moving the fuel line away from the front of the block when it runs from the fuel pump up to carb- is close to block and soaks up a lot of heat-

sometimes it will start if vapor locked if you shoot a little starting fluid or gas in carb- creates vacuum and breakks vapor lock
 
I got back a few hours ago and am settled back in. It didn't sputter, miss or cut out on me once. All the way up and all the way back. It did fine. I did move the fuel line away from near the block, water pump, and alternator and put it on the fender well, running it over the alternator with a bracket I made. It did great until I punched it close to home. Then it died, but came back to life before I came to a stop. I'm' thinkin maybe the post was right about winter fuel is begging too much to vaporize and since it is around 70 degrees when it vapor locks, that may be what is doing it.

Would a cap fix this situation? I have an old old ooooooooooooold locking gas cap on there that never caused a problem before, but maybe it is tooo old!

I haven't found a good cap replacement yet. The one I ordered the guy at the parts house said it was an OEM when I ordered it. When I went to pick it up, it wasn't OEM!!! Argh! I hate that.

Anyway, anyone know a good place to get an OEM gas cap for my Duster (1970)

Why did someone say an electronic fuel pump would be a solution? What is the difference between the mech. one I have on there and an electric one? Would it be the location it is in that would keep it from getting hot like the mechanical one?

Thanks!:cheers:
 
Gas cap probably isn't your issue. If you had problems, then opened the gas cap and then your problem was gone, it would be suspect.. I've seen it before where they don't vent or don't hold vacuum correctly on some designs and it can cause issues.

Couple things with an electric pump:
1. If fuel is boiling in the line before the mech pump, then it can be tough for the mech to get a prime and deliver fuel.
2. If the fuel is boiling after the pump and not filling the bowls, the increased and constant pressure from an electric can reduce fuel evaporation. Turning into a gas is a function of pressure and temperature. Higher pressure means you need more temperature before it boils (this is why water boils at lower temperatures at high altitude).

Without a return style regulator, it can be tough to build enough pressure to prevent boiling, but the steady nature of the pressure helps. There are return less style regulators, but they seem to be of questionable performance - they can help build a little more pressure just prior to the carb though.

If everything seemed to run well except WOT once it was good and warm, then I'd begin to suspect something much much simpler: float levels. If the fuel level in the bowl is too low, it will be tougher to start warm (even less gas left after the engine cools), it will stumble on moderate to full throttle, and can contribute to other issues.

Proper float level is dependent on the model of the carb. It's also very easy to adjust, but shouldn't be done blindly. Measure properly and document the changes. Also have a few good gaskets on hand in case you break one tearing into it 😉
 
The reason a REAR mount electric pump can help over OEM is that the feedline is not under a vacuum. The pressure in the feedline with the pump in the rear raises the boiling point of the fuel. There of course, are limits.

"So far as the cap" remember that NO FACTORY CAP provides the vent function. In 69/ earlier cars, the vent was near the top of the fill tube.

In 70 cars with evap, and later, the vent was the 1/4 line to the front, and either that must be kept open, or else something else to replace it as the vent

The evap equipped cars ALL had what are called "pressure vacuum" caps, which allow "some" pressure to build, as well as "some" vacuum to occur, before "relieving" thepressure.

These are a PITA because changes were made over the years. There's a couple of threads on these caps

Here

http://www.forabodiesonly.com/mopar/showthread.php?p=1970887599
 
67Dart273 said:
The reason a REAR mount electric pump can help over OEM is that the feedline is not under a vacuum. The pressure in the feedline with the pump in the rear raises the boiling point of the fuel. There of course, are limits.

"So far as the cap" remember that NO FACTORY CAP provides the vent function. In 69/ earlier cars, the vent was near the top of the fill tube.

In 70 cars with evap, and later, the vent was the 1/4 line to the front, and either that must be kept open, or else something else to replace it as the vent

The evap equipped cars ALL had what are called "pressure vacuum" caps, which allow "some" pressure to build, as well as "some" vacuum to occur, before "relieving" thepressure.

These are a PITA because changes were made over the years. There's a couple of threads on these caps

Here

http://www.forabodiesonly.com/mopar/showthread.php?p=1970887599
Click to expand...

Agreed on all points. The pump should be located as close to the supply as possible since most all pumps, electric especially, don't suck very well, and pressure is pressure. The regulator should be as close to the carb as feasible if it's going to help with boiling.

On the cap, it shouldn't matter unless things have been modified over the years, or you're unsure of the presence of any vent. Some get capped by well meaning previous owners, some get clogged.. And finding a proper cap is a pain. That, and it's only a remote possibility that can be tested by popping the cap open IF you have issues with it staying running down the road.

Sounds like that's no longer a problem though, but duel supply at WOT might be. The improvement after rerouting the hoses points to one of the problem being the heat applied to the line when warm.
 
I have not seen where you have actually diagnosed that you are experiencing vapor lock. If you don't confirm what you suspect, you will be chasing your tail.
 
Another plus for the electric pump is that there is fuel in the carb instantly when the engine is started instead of the engine having to crank to make the pump function before it delivers fuel to the carb.
 
Install heat sheild around the fuel line coming to the pump and from the pump. Especially where it runs between the header and the frame rail. Manual pump cannot pump boiling ethanol. You can buy rols of it at any speed shop. You can see it on my fuel line below it is a silver slip on heat sheild.
 

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Steve, mail me your engine when you get a minute, will ya?
 
RustyRatRod said:
I have not seen where you have actually diagnosed that you are experiencing vapor lock. If you don't confirm what you suspect, you will be chasing your tail.
Click to expand...

Right after it stalled while driving 65 down the highway, then restarted in like 2-3 seconds, I pulled into a gas station and pulled the delivery line from the fuel pump. It burst a blast of gaseous air and then dribbled fuel. Is this not vapor lock?

Thanks
 
Oldmanmopar said:
Install heat sheild around the fuel line coming to the pump and from the pump. Especially where it runs between the header and the frame rail. Manual pump cannot pump boiling ethanol. You can buy rols of it at any speed shop. You can see it on my fuel line below it is a silver slip on heat sheild.
Click to expand...

This is my next step as I see it. I think the problem is the fuel itself. I never had this problem before running mopars for 30 years. 33 years. The fuel lines and pumps have remained the same the whole time. Just now it started happening out of the blue. I will get some heat shield and put it between the header and the fuel line, and where it comes up between the alt, water pump and block. I re-routed it to go around that location and it helped a lot. Still have prob at WOT when it runs the fuel out of the bowls. It died again, but only long enough to get fuel to the carb again. It is either the fuel bowl adjustment or the ethanol evaporating too soon. But I really do think it is the ethanol.

Thanks...
 
Phreakish said:
Gas cap probably isn't your issue. If you had problems, then opened the gas cap and then your problem was gone, it would be suspect.. I've seen it before where they don't vent or don't hold vacuum correctly on some designs and it can cause issues.

Couple things with an electric pump:
1. If fuel is boiling in the line before the mech pump, then it can be tough for the mech to get a prime and deliver fuel.
2. If the fuel is boiling after the pump and not filling the bowls, the increased and constant pressure from an electric can reduce fuel evaporation. Turning into a gas is a function of pressure and temperature. Higher pressure means you need more temperature before it boils (this is why water boils at lower temperatures at high altitude).

Without a return style regulator, it can be tough to build enough pressure to prevent boiling, but the steady nature of the pressure helps. There are return less style regulators, but they seem to be of questionable performance - they can help build a little more pressure just prior to the carb though.

If everything seemed to run well except WOT once it was good and warm, then I'd begin to suspect something much much simpler: float levels. If the fuel level in the bowl is too low, it will be tougher to start warm (even less gas left after the engine cools), it will stumble on moderate to full throttle, and can contribute to other issues.

Proper float level is dependent on the model of the carb. It's also very easy to adjust, but shouldn't be done blindly. Measure properly and document the changes. Also have a few good gaskets on hand in case you break one tearing into it 😉
Click to expand...

I will try WOT without the gas cap and see if that solves the problem. If not, there is heat shield that is less expensive than an electric fuel pump with regulator, but if I gotta I gotta. Thank you for taking the time to explain it all. I appreciate it... Oh, BTW it starts hot with no problem now.
 
mguner said:
A good insulator gasket under the carb, make sure the exhaust manifold on the passenger side does not have a stuck EFE valve, you can also insulate and check routing of fuel line under the hood to reduce heat transfer to it.
Click to expand...


Running a performer by edelbrock. Don't see an EFE valve. But did re-route the fuel line and it helped a lot. Tremendously as a matter of fact. Now I have to figure out why it cut out after WOT running the bowls empty, then started again before I stopped.

Thanks...
 
middleagecrisis said:
FWIW, The clear filters will not fill completely up with fuel when the motor is running. Half full is all I've ever observed when running, and I never had any issues with fuel starvation. Primary symptom of vapor lock is hard starting after the car has set hot for a few minutes. Are you having this problem?
Click to expand...

When I was bracket racing back in the '70's I used a Holley electric fuel pump, fuel pressure regulator mounted on the passenger side fender, then a "Y" to two clear fuel filters, each one going to the front and rear fuel bowl of a Holley Double pumper. When I added an aluminum cool can in fuel line before the regulator, I experimented with both dry ice and then regular ice in the cool can (dry ice was too expensive). The end result with regular ice was that the clear filters went from looking half full to looking completely full! That cooler fuel in the lines must have been able to purge out the vapor that normally hides in the fuel filters. Horsepower increase? Who knows, but never experienced vapor lock.
 

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After re-routing the fuel line, it is not hard to start when hot now. It was very hard to start before re-routing the fuel line to avoid going up the front of the motor.

I could try a cooling can, but for long trips it may not be practical. It would work for around here on hot days though. We get 100+ during the summer, though I don't like to drive it in that hot of weather.

I haven't had the opportunity to try running WOT without the gas cap yet.

There is a vent at the top of the filler tube inside the trunk. It is not open. Is it supposed to be?? There is also a vent tube at the sending unit that is not open. Is that supposed to go to a vented filter?

Thanks!
 
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