318 Can't keep fuel in filter, stalls when hot.

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Dodge72

Dodge72

Odd one out
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Hello!

Alright so my boyfriend and I are trying to figure this one out and it has us scratching our heads. He's got a 67 Dart with a 78 318/904 combo. Budget junkyard rebuild, new seals and bearings with a 340-esque cam. Mechanical fuel pump and stock tank.

He's been driving it as is for a few months and it's been great. We decided to head down to Woodburn and that was a 2.5 hour drive down the 5. When we arrived and waiting in line to enter, his Dart dies. He struggles to get it started and it does this multiple times before we parked. It was a real struggle going into traffic on the way home. We put a heat sleeve on the fuel line by the header tube, tied it further away, and changed the in line fuel filter. We noticed it was bubbling into the filter and it was barely filling up. It still had issues but we managed to all get home.

It's completely fine when cold. The filter fills up. He drives it around for approximately 15-20 minutes with 0 issues. We've gone around the neighborhood multiple times, stopping and all that. We've noticed the filter ever so slowly loses its fuel level over the course of maybe half an hour to 45 minutes. It eventually gets to the point where there's not enough fuel in the filter and it sputters, backfires, and dies: but dies only in gear. Hard to start.

He's done multiple things and we're still left confused. Here's what's been done :

-New fuel tank (he had it already)
-Blew out fuel lines with compressed air and some brake cleaner (nothing in there)
-New fuel pump installed, twice. (no change)
-Changed the fuel filter
-Bent the hard fuel line even further away from the header
-Cleaned out the carb (650 cfm AVS. Had some dirt in the bottom but filters were okay)
-Got a new vented gas cap
-Blocked off the vent on the gas tank
-Ran the car with the mechanical fuel pump but ran it from a gas can. While we didn't wait to see if it stalled completely, the fuel filter did not fill up or change. It began to run a little rough in gear and we shut it down. That tells me it's nothing to do upstream of the fuel pump and that leaves the fuel pump, eccentric, lines, and carb.

He's got it to stop bubbling into the filter (maybe solved a boiling issue), but it's barely pumping into there. My Dart has the filter almost full the entire time (also mechanical). The odd thing is the little fuel pressure gauge consistently reads 6 psi, even when there's almost no fuel in the fuel filter that's down stream of it.

Could the used fuel eccentric have failed? We can see its got a bit of wear but he hasn't torn the front part of the engine to remove it. What else can we test? Any help is appreciated. He may chime in on here to answer questions as well. (@Byron Gray).
 
I don't know, but why block the vent on the gas tank? Seems it needs all the venting it can get.

I tell you, REAL vapor lock is rare but it sounds like that might be it. I would just try to isolate every stretch of fuel line completely away from any heat source.

Lastly......try some non ethanol fuel and see if that makes a difference. He may have run into some fuel that had a higher content and boils more readily.
 
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Dodge72 said:
kay)
-Got a new vented gas cap
-Blocked off the vent on the gas tank
.
Click to expand...

I don't know why you'd do that the stock vents worked just fine, and using a vented cap leaves you open for fuel puking all over the fender on a hot day when near full

======================================

This sounds like a classic modern alky fuel heat problem. Modern fuel boils easier than old "pure" gas.

Putting the sleeve over the tube MAY have just trapped heat in.

Best thing I did before going to EFI was

Installing a rear mount electric pump and ditching the mechanical
Building a vapor return system using a Wix filter with a return orifice
Using thick isolator gasket under the carb

If you think its the pump/ eccentric you need to get a pressure gauge and do both a volume and pressure test of the pump

I would DOUBLE check that the tank is actually venting and I'd check the tank pickup sock for blockage, blow out the line if you have not and check for line blockage. How about the condition of the flex hose from tank to tube?
 
Greetings from across the river. Duel rear exhaust? I noticed on my passenger side the tube up over the rear is close-ish to the fuel line. Might shield that too. What about the pick up sock? You also mention regulator at 6psi but no fuel, did you temporarily remove the regulator and see if that helped? Lastly needle and seat, I can't see where they fail closed but its worth the look.
 
67Dart273 said:
Installing a rear mount electric pump and ditching the mechanical
Building a vapor return system using a Wix filter with a return orifice
Using thick isolator gasket under the carb
Click to expand...

^^^ This. Even a $15 Facet 'jiggler' pump will supply all the 318 needs. Makes cold starts a breeze too with a full fuel bowl. Wire it to ACC and itll turn off when you take your keys with you.
FACET ELECTRONIC FUEL PUMP 12 VOLT 4129204 | eBay

If you want to check the eccentric. just pull the pump and stick a screwdriver in there to lay across the eccentric and bump the motor or turn it slowly and observe the movement of the screwdriver. It could be flopping around in there, but thats a longshot.
 
67Dart273 said:
I don't know why you'd do that the stock vents worked just fine, and using a vented cap leaves you open for fuel puking all over the fender on a hot day when near full

======================================

This sounds like a classic modern alky fuel heat problem. Modern fuel boils easier than old "pure" gas.

Putting the sleeve over the tube MAY have just trapped heat in.

Best thing I did before going to EFI was

Installing a rear mount electric pump and ditching the mechanical
Building a vapor return system using a Wix filter with a return orifice
Using thick isolator gasket under the carb

If you think its the pump/ eccentric you need to get a pressure gauge and do both a volume and pressure test of the pump

I would DOUBLE check that the tank is actually venting and I'd check the tank pickup sock for blockage, blow out the line if you have not and check for line blockage. How about the condition of the flex hose from tank to tube?
Click to expand...
So the tank I put in looks like this. That port on top that I thought was a vent started leaking gas out if it when I filled it up. So I think that was for a return line and not a vent thats why I put a cap over it so I wasn't leaking gas. It looks more like what you slip the rupper hose over.
I blew out the line the rubber hose from the sending unit to the hardline is no more then 2 inches long and I replaced a few months last time I was under there still looks good.

Screenshot_20210808-223001_Chrome.jpg
 
dano said:
Greetings from across the river. Duel rear exhaust? I noticed on my passenger side the tube up over the rear is close-ish to the fuel line. Might shield that too. What about the pick up sock? You also mention regulator at 6psi but no fuel, did you temporarily remove the regulator and see if that helped? Lastly needle and seat, I can't see where they fail closed but its worth the look.
Click to expand...
I removed the regulator I had in it and I have the edelbrock fuel line off the carb that looks like an L that comes out from under the choke it has a port to thread in an in line pressure gauge
 
Dana67Dart said:
Does this look familure?

https://photos.app.goo.gl/RbX6ALGtTBDr2owu5

Note the temp of the filter at the end 151 deg

IIRC alcohol fule vaporizes at 140 something.

I switched to non alcohol fuel problem gone, no other changes.

Thought your description sounds a bit more extreme
Click to expand...
That basically looks like what mine is doing. I have a temp gun but battery is dead so haven't been able to read Temps.
 
My 67 273 2 brl. did the same thing. Repeating cycle viewed in plastic filter once the engine was hot. Took a while to realize the filter never was actually empty. It was full of vapor. Carb bowl was too. When the needle would open the vapor would go and some liquid fuel would come into the filter.
73 and later have the fuel filter positioned vertically down near the pump and a thicker gasket under the carb. Those changes cured mine. I did find where to buy real gas a short time later. I had enough trouble with fuel lines on the weed wacker, etc.. so everything here with a carburetor now gets real gas.
 
As well as everything else mentioned, put an insulator gasket under the carburetor if you don’t already have one. Eliminate any high spots in the line if possible. Also, have you replaced all the original rubber fuel line on the way to the pump?
 
Check out the fuel bowl in the carb now.

Bowl vent, needle n seat.

Eccentrics dont really fail, they come loose on rare occasions...but none on my clock.

Something else is going on...and I have read what you've done so far.

So maybe the pickup/line has caught something and its acting like a one way valve.
 
Do you have your bowl vent plugged in the carb? Run this to air cleaner....Not sure if AVS had vents outboard of the step up pistons. Those plastic filters will never get a full fuel fill horizontally because of the air gap on top over both ends, air can only compress so much under 4psi. Run that filter vertically if possible..
AVS.jpg
 
You can verify that your fuel pump is pumping enough volume by having the output line send fuel into a container, but you might need to rig something up to keep fuel going into the carb to have it run long enough.

Warm the car up a bit and then disconnect the high pressure line and attach a hose that dumps into a container. run the motor for 15 seconds( if it will do so). That might be long enough to determine the volume is sufficient.

Install a 3 nipple fuel filter and run a return line to the tank. It will allow the fuel to circulate a bit more and help bleed off the sir pockets. Be sure to point the 3rd nipple upwards.

Insulate and/or relocate any fuel line that is near a heat source, especially to and from the fuel pump and carb.

Verify that you have adequate fuel tank venting with your fuel cap by blowing low pressure air into the currently plugged tank vent.

As mentioned above, add a phenolic spacer to keep heat out of the carb. If you live in a relatively warm area, pull the manifold and block the heat crossover as a last resort. I haven't run one here in California for decades. I wouldn't do this in some other states that get too cold.
 
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I’ve worked on similar that had a rubber fuel hose collapsing on the way to the pump.
 
BTW, I have no carb spacer, I did not relacate the filter, or any lines. No return vent on the filter I just switched out to non alcohol fuel.

My problem was solved.

Another BTW...

The engine will idle for quite a while on the fuel in the bowel. As my video shows.

The empty or emptying fuel filter has vapor in it pressurized at 5 to 7 psi. The float is still high and is not needing to allow any more fuel in to the bowl. Once the float sinks enough the vapor is released pressure is around 2 to 3 and fuel flows to fill the filter and the bowel till full and the needle seats and the cycle repeats.
 
Check the two jumper hoses
I've had issues with both, the rear one collapsing under its own vacuum, the front one collapsing when the rubber got hot from the engine bay heat
 
Byron Gray said:
So the tank I put in looks like this. That port on top that I thought was a vent started leaking gas out if it when I filled it up
Click to expand...

Ok a 67 should have a dedicated vent line welded into the filler neck up in the trunk. This should have a tube going up and over up high near the quarter "top" and back down along the filler tube, through the gasket, and open ends into the rear frame rail. THAT IS the vent

that newer tank having the extra line COULD BE USED FOR a vapor return There are at least 3 or 4 Wix filters, different sizes, with a built in vapor port.
 
This filler tube is not from a 67 dart but is a good representation of what your filler neck and vent should look like

16285566826686770062323123086634.jpg
16285566989334721657538866091767.jpg


This is from the inside of the trunk of a 67 dart
16285567570531727471058228025515.jpg

Note the 4 holes for mounting

16285568577935210108398667530404.jpg


This is what the stock cap should look like. ( This is a CAP car to boot, no venting in the cap)

16285570210703756120584069659436.jpg
 
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Sorry for the late reply ben busy on my other car. Haven't fixed the issue yet and yes my vent line is off the filler neck tube like in the pictures but I think at some time it may have broken off under the car. I took it out to clean out the vent it was plugged up. I have it disconnected from the vent tube right now.
 
Byron Gray said:
. Haven't fixed the issue yet and yes my vent line is off the filler neck tube like in the pictures but I think at some time it may have broken off under the car
Click to expand...
The stock vent is short and is not visable under the car
Byron Gray said:
I took it out to clean out the vent it was plugged up.
Click to expand...
Plugged vent is not good I assume you cleaned it out.
Byron Gray said:
I have it disconnected from the vent tube right now.
Click to expand...
Be careful, no vent and you could collapse your gas tank. Uncapped vent in your trunk and you could blow up. (Disclaimer all worst case scenarios)
 
Reading all the comments and the first thing that comes to mind is the tank is under a vacuum. Open the car when it is acting up and see if you then get fuel. The pump will pull fuel until it runs out of air in the tank, then creates a vacuum to where it will not pull anymore fuel.
 
I agree with loosening cap when it starts acting up.
And you are better off to wrap the header instead of the fuel line. Im running a el cheapo facet pump on my 360/thermoquad and it seems to provide enough fuel. If i let it idle too long when its hot, it will start running rough and pump gets loud. Like its running out of fuel. I think its vapourizing.
 
Dodge72 said:
Hello!

Alright so my boyfriend and I are trying to figure this one out and it has us scratching our heads. He's got a 67 Dart with a 78 318/904 combo. Budget junkyard rebuild, new seals and bearings with a 340-esque cam. Mechanical fuel pump and stock tank.

He's been driving it as is for a few months and it's been great. We decided to head down to Woodburn and that was a 2.5 hour drive down the 5. When we arrived and waiting in line to enter, his Dart dies. He struggles to get it started and it does this multiple times before we parked. It was a real struggle going into traffic on the way home. We put a heat sleeve on the fuel line by the header tube, tied it further away, and changed the in line fuel filter. We noticed it was bubbling into the filter and it was barely filling up. It still had issues but we managed to all get home.

It's completely fine when cold. The filter fills up. He drives it around for approximately 15-20 minutes with 0 issues. We've gone around the neighborhood multiple times, stopping and all that. We've noticed the filter ever so slowly loses its fuel level over the course of maybe half an hour to 45 minutes. It eventually gets to the point where there's not enough fuel in the filter and it sputters, backfires, and dies: but dies only in gear. Hard to start.

He's done multiple things and we're still left confused. Here's what's been done :

-New fuel tank (he had it already)
-Blew out fuel lines with compressed air and some brake cleaner (nothing in there)
-New fuel pump installed, twice. (no change)
-Changed the fuel filter
-Bent the hard fuel line even further away from the header
-Cleaned out the carb (650 cfm AVS. Had some dirt in the bottom but filters were okay)
-Got a new vented gas cap
-Blocked off the vent on the gas tank
-Ran the car with the mechanical fuel pump but ran it from a gas can. While we didn't wait to see if it stalled completely, the fuel filter did not fill up or change. It began to run a little rough in gear and we shut it down. That tells me it's nothing to do upstream of the fuel pump and that leaves the fuel pump, eccentric, lines, and carb.

He's got it to stop bubbling into the filter (maybe solved a boiling issue), but it's barely pumping into there. My Dart has the filter almost full the entire time (also mechanical). The odd thing is the little fuel pressure gauge consistently reads 6 psi, even when there's almost no fuel in the fuel filter that's down stream of it.

Could the used fuel eccentric have failed? We can see its got a bit of wear but he hasn't torn the front part of the engine to remove it. What else can we test? Any help is appreciated. He may chime in on here to answer questions as well. (@Byron Gray).
Click to expand...

My Dad had the same thing happen on the 67 as well. It would boil the fuel or vaper lock it. I tried wrapping it but seemed to make it worse. I then ran fuel line on outside of frame up trough front of grill and then back to carb this helped a lot I also added a second electric fan and swapped out to a holley over edlebrock carb. Seems to have fixed it. Now we have wiring issues to deal with.
 
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