1957 Ford 640 Vapor Lock?

raxxter

Member
Is the visibly low fuel level and bubble(s) in the pictures caused by vapor lock?

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I have a new, occasional, issue that I think I ve finally found the cause of.
I have a 1957 Ford 640, 12V conversion, that starts and runs just fine for a while. Around the 15-20 minute mark, it will sometimes -sometimes- stumble and slowly die. When I engage the clutch, it will sometimes catch and start running just fine. Other times, when it dies, it will immediately start right back up and run just fine for the rest of the time I m doing chores around another 20 or so minutes.
Then there are times where it won t start again for 5-10 minutes, and then it seems to run fine.

I recently replaced the carburetor (all of this in an effort to address this problem), pulled and cleaned the fuel tank, replaced the fuel shut off valve and the associated filter screen that is up in the fuel tank, blew out the fuel line, which didn t appear to be restricted in any way, and I replaced the sediment bowl.

I also converted the tractor to a 12V system, and installed an electronic ignition. I know it s not the fuel cap on the tank, as I have the original that came when I bought the tractor and a new one that makes a poor seal as it allows fuel to spill on bumpy rides with a full tank.

Today I noticed the gap where the fuel is sitting in the bowl lower than the top.

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Is this some sort of vapor lock? Has anyone seen this before, and more importantly, fixed it?
It doesn t seem to happen an more or less with temperature or weather. I am beginning to wonder if it might not happen more often when the tank is half full or less. Less fuel to assist the gravity feed of the fuel to the sediment bowl?

Any help would be appreciated.

-Raxx

P.S.: A couple of pics of the fuel line, in case that helps?

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It is not vapor lock. Vapor lock happens on a system with a fuel pump were there is air in the line between the tank and the pump so the pump cannot prime. That tractor has a gravity feed system, so no vapor lock is possible. That small amount of air at the top of the sediment bowl is normal and will not cause any issue with fuel delivery. If it starts and runs with that small amount of air at the top of the glass then it should contuinue to run until the tank is empty. Your issue sounds like the coil may be going bad.
 
(quoted from post at 20:25:40 04/30/20) It is not vapor lock. Vapor lock happens on a system with a fuel pump were there is air in the line between the tank and the pump so the pump cannot prime. That tractor has a gravity feed system, so no vapor lock is possible. That small amount of air at the top of the sediment bowl is normal and will not cause any issue with fuel delivery. If it starts and runs with that small amount of air at the top of the glass then it should contuinue to run until the tank is empty. Your issue sounds like the coil may be going bad.

Sean-
Thanks, and as soon as I read your response, I realized it's not vapor lock....but some other reason fuel may not be flowing?

The thing is, that fuel gap is not always present. When I noticed it today, I got it started again (it was one of those sometimes where it didn't start right away) immediately after I put my mouth to the tank opening and blew into it to give the fuel a little encouragement to flow down the fuel line. After trying that, the gap had disappeared and it started right up. Ran for another 15 minutes, died, gap was back, ate dinner, gap gone, started up, and parked it for the day.

And while it does sound like a coil, it has a brand new coil on it today. The third one. The first 12V one was a Pertronix that failed, the second was a Napa one that was on it today before I put the Pertronix replacement on it hoping it wouldn't stall out again. If it was the coil, that would mean both the Napa and the replacement Petronix were bad in the exact same way. Possible, but I think I'll continue to investigate other causes first.

By any chance, do you have a 600 series that shows a gap like the one in the photos? Is that normal?

Thanks,

Raxx
 
I would try moving the fuel line from where it is now. The factory has them coming down right in the center of the manifold. I ran mine in front of the exhaust manifold but i think the way the factory has it heats the fuel a little for better vaporization. It looks to me like you are getting a lot of vapor from the position of your line. I'll bet you can't hold your fingers on the line down by the bowl unless they're calloused real good.
 


Your filter bowl is not installed as original. Check the path through the mounting bolt and into the carb for a restriction.
 
Vapor-lock requires high suction to lower the boiling point of the fuel. Impossible with a gravity feed system.
 
That's because the carburetor is an aftermarket replacement with non original inlet port.

Dean
 
All the symptoms sound like a fuel problem don't they? You have eliminated that. It's a weak spark probably from a failing coil. I had almost the same issues with my NAA several years ago. Once I replace the coil it never happened again.
 
The fuel line looks real close to the exhaust manifold to me. Could it be that after she runs for the 15-20 minutes the manifold heats the line and causes the fuel to start to vaporize? Wild guess maybe..

Perhaps when she starts to die, squirt that part of the line with water in a Windex type bottle and see what happens. Ya don't want put too much on the manifold tho, hot cast iron and water are not the best of friends.
 
(quoted from post at 03:25:40 05/01/20) It is not vapor lock. Vapor lock happens on a system with a fuel pump were there is air in the line between the tank and the pump so the pump cannot prime. That tractor has a gravity feed system, so no vapor lock is possible. That small amount of air at the top of the sediment bowl is normal and will not cause any issue with fuel delivery. If it starts and runs with that small amount of air at the top of the glass then it should contuinue to run until the tank is empty. Your issue sounds like the coil may be going bad.

I have the same problem with my 860. I have replaced the coil, points, condensor, plug wires, carb, pulled and cleaned the gas tank and replaced the shutoff with screen. Going broke and it still does the same thing. Open to suggestions.
 
Thank you for all of the input and the suggestions.

Sorry for the delay getting back to this work, life, etc.

I m pretty positive the fuel line is not original, nor run in the original path. I did purchase a replacement fuel line (I think from this site), but it doesn t fit. It s the one that resembles the letter "P". It might be made for a fuel tank with a different outlet? I think I ve read somewhere that there are tanks with front outlets and center outlets?

The thing is, it s the same fuel line, run the same way, that was on the tractor when I purchased it. The first summer I had it, it would run all day with no issues. Which kinda makes me think it s not really the fuel line.
I only suggest vapor lock as my hair was starting to not grow back where I was constantly scratching my head trying to figure out the problem.

Like Wisconsin Willie, I ve replaced pretty much everything other than the tank itself and the fuel line, and I still have problems

-Raxx
 


While not technically vapor lock, still could be fuel boiling in the line,, creating bubbles and pressure and slowing down the fuel flow,,,, to almost nothing. In a gravity fed system, the bubble will automatically vent slowly upwards.... up to the tank if there is no high spot in the fuel line routing. So it will slowly self correct. As others said, the fuel line is routed incorrectly and that would be my first fix.

Fuel pumps were added to pressurize the fuel to help keep it from boiling. Thats why early fuel pumps were mounted low in engine compartment.. although the cam location has a lot to do with it. High mounted fuel pumps create more of problem and a possible fuel hazard by leaking pressurized fuel on the manifold, where a bottom mount fuel pump simply dripped on the ground. also made an excellenct place to put a water trap.
 
(quoted from post at 10:54:31 05/02/20) Thank you for all of the input and the suggestions.

Sorry for the delay getting back to this work, life, etc.

I m pretty positive the fuel line is not original, nor run in the original path. I did purchase a replacement fuel line (I think from this site), but it doesn t fit. It s the one that resembles the letter "P". It might be made for a fuel tank with a different outlet? I think I ve read somewhere that there are tanks with front outlets and center outlets?

The thing is, it s the same fuel line, run the same way, that was on the tractor when I purchased it. The first summer I had it, it would run all day with no issues. Which kinda makes me think it s not really the fuel line.
I only suggest vapor lock as my hair was starting to not grow back where I was constantly scratching my head trying to figure out the problem.

Like Wisconsin Willie, I ve replaced pretty much everything other than the tank itself and the fuel line, and I still have problems

-Raxx
egarding your "air gap", I expect that it is due to the not level position of sediment bowl assy. See marked up picture. Fuel enters in center but exits from off center. For air to escape it must either go into carb from off center exit (which it can't since fuel covers that exit) or bubble back up the inlet line to tank and that would still allow the trapped air in the "air gap" with no escape route. Maybe a minor leak at bowl gasket or bouncing about over rough ground will sometimes allow air escape. If you loosen the bowl retainer the air gap will probably disappear as air escapes and fuel forced in. I don't expect this to cause a running problem.
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Raxxter, Back to basics. When it dies perform two checks. immediately check for spark by removing a plug and holding it against a ground. Second, but it doesn't need to be immediately, is to check the level of the gas in the float chamber. This is done by removing the drain plug in the bottom of the float chamber and replacing it with a barbed adapter with some clear vinyl tubing pushed onto it. When the tubing is routed up beside the carb it shows you the level of the gas in the float chamber.
 
While technically true that a gravity feed system is hard to vapor lock because the bubbles just flow uphill to the tank.
It is also true that gasoline starts boiling (turning from a liquid to a gas) at temperatures below 100 degrees F.
This can disrupt gasoline flow to the point that a lay person calls it vapor lock.
 
(quoted from post at 17:56:00 05/02/20) While technically true that a gravity feed system is hard to vapor lock because the bubbles just flow uphill to the tank.
It is also true that gasoline starts boiling (turning from a liquid to a gas) at temperatures below 100 degrees F.
This can disrupt gasoline flow to the point that a lay person calls it vapor lock.
call" is the key word there!
Ray J. Johnson is to become annoyed when addressed as "Mr. Johnson," exclaiming in a loud voice, "My name is Raymond J. Johnson Jr. Now you can call me Ray, or you can call me J, or you can call me Johnny, or you can call me Sonny, or you can call me Junie, or you can call me Junior; now you can call me Ray J, or you can call me RJ, or you can call me RJJ, or you can call me RJJ Jr. . ." ultimately ending with, "but you doesn't hasta call me Johnson!" ....or vapor lock.
 
JMOR:

Thank you for the picture. I understand the fuel both enters and leaves the sediment bowl from the top. That s why I was thinking the air bubble, while present, would prevent the correct amount of fuel from flowing to the outlet of the bowl and into the carburetor. I can t think how the air is getting into the bowl, unless it s somehow being sucked back in from the carburetor?
And loosening the bowl would be a quick fix for getting rid of the bubble, I m to not have to keep jumping off the tractor to allow the air to escape and/or having fuel leak from the bowl.
Oh, and the bowl doesn t sit level. It s as level as it can get. Right now the bowl is resting against the carburetor. Maybe later I can get a few more pictures.

Showcrop:

Definitely back to basics. I think I ll start carrying a spark tester and use that as soon as it dies.
And love the idea of the fluid level monitoring using a bend of plastic tubing. I m heading down to the hardware store for a barbed fitting, some tubing, and something (hose clamps, maybe?) to hold the tubing in an exaggerated "S" so the level will vary and it will keep the dust out.

Thanks again, all. I ll post updates/results as I get them (and time).

-Raxx
 
Ok, Ok...can I be excused the term 'vapor lock'? :oops:

How about 'improbable bubble'? 'Incongruous fuel system' (knowing full well it could be fire instead or fuel, but still suspecting fuel)?
 
(quoted from post at 19:16:00 05/02/20) Ok, Ok...can I be excused the term 'vapor lock'? :oops:

How about 'improbable bubble'? 'Incongruous fuel system' (knowing full well it could be fire instead or fuel, but still suspecting fuel)?
ecause of where the air pocket is relative to the outlet, as I said before, I don't expect it to block flow into carb. The bowl fuel level should confirm that.
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It is also true that gasoline starts boiling (turning from a liquid to a gas) at temperatures below 100 degrees F.

The boiling point of gasoline is around 200 degrees Fahrenheit, not 100 degrees.
 
Sean; If you look at the MSDS for gasoline you will see it has a boiling point of 85 to 437 degrees F.
This is because gasoline is made up of different things that boil off at different temperatures.
This is why we have summer and winter gasoline.
Because winter gasoline will boil off to easy in the heat of summer.
It is also why if you set a can of gasoline out in the sun it will blow up like a pregnant sow.
Adding ethanol to the gasoline just makes it worse.

I also seem to remember a poster here doing a test a few years back.
He put a bowl of gasoline in water and heated the water to see when the gasoline would start to boil.
If I remember correctly visible bubbles started at about 100 degrees and a full rolling boil was at about 25 degrees more.
Hopefully he still post here and can comment on it.

But with all that aside it is a fact that gasoline will boil and vaporize causing vapor lock at engine temperatures and very few older engines ever saw 200 degrees.
But to have true vapor lock you need a system to where the vapor gets trapped in the system.
That is pretty much impossible in a gravity system with out bends of loops in the gas line to where the vapor has to travel down hill in the system so it gets stuck at the high point.

What most are calling vapor lock on the old Ford tractors is actually fuel boiling; and with the vapor bubbles trying to make their way uphill to the tank; it disrupts the flow of the gasoline trying to flow downhill so the carburetor starves for gasoline.

So while some will say the system can not vapor lock; and be correct; making that comment just confuses the lay person trying to figure out why his tractor keeps dying.
 
(quoted from post at 01:59:24 05/03/20) Sean; If you look at the MSDS for gasoline you will see it has a boiling point of 85 to 437 degrees F.
This is because gasoline is made up of different things that boil off at different temperatures.
This is why we have summer and winter gasoline.
Because winter gasoline will boil off to easy in the heat of summer.
It is also why if you set a can of gasoline out in the sun it will blow up like a pregnant sow.
Adding ethanol to the gasoline just makes it worse.

I also seem to remember a poster here doing a test a few years back.
He put a bowl of gasoline in water and heated the water to see when the gasoline would start to boil.
If I remember correctly visible bubbles started at about 100 degrees and a full rolling boil was at about 25 degrees more.
Hopefully he still post here and can comment on it.

But with all that aside it is a fact that gasoline will boil and vaporize causing vapor lock at engine temperatures and very few older engines ever saw 200 degrees.
But to have true vapor lock you need a system to where the vapor gets trapped in the system.
That is pretty much impossible in a gravity system with out bends of loops in the gas line to where the vapor has to travel down hill in the system so it gets stuck at the high point.

What most are calling vapor lock on the old Ford tractors is actually fuel boiling; and with the vapor bubbles trying to make their way uphill to the tank; it disrupts the flow of the gasoline trying to flow downhill so the carburetor starves for gasoline.

So while some will say the system can not vapor lock; and be correct; making that comment just confuses the lay person trying to figure out why his tractor keeps dying.
ell, John, it is all still here from 2012, but will probably just stir the pot for a few. Personally, I'm looking forward to carb bowl fuel level measurement results. Expecting to "bubble/gap" to be vindicated. :)
http://ytforums.ytmag.com/viewtopic.php?t=905685
 
I had the same problem on my 860 as the fuel line is fed down between the block and the manifolds to the carb. After changing the carb, removing the gas tank
and installing a new shutoff and screen, installing a new coil/points/condenser and plug wires and still having the problem, I took the temp gun and shot it on
the fuel line behind the manifold. 279 degrees F. I made a wrap out of aluminum foil and installed it around the fuel line (not an easy task given the location)
and it hasn't bothered since. So, whether you call it vapor lock or fuel boil, it is the problem. My grandfather bought the tractor new and it was only the last
couple of years that the problem surfaced. It was possibly related to my switching to premium gas in order to get away from ethanol-related gum-up, as the
tractor sits for months unused. The higher the octane, the more volatility and likelihood of vaporizing. In the attached photo you'll see that the foil comes
all the way down to the sediment bulb. It wouldn't have to, as the problem is up by the exhaust manifold (I took the temp just below, between the exhaust and
intake), but in order to feed it up along the line I had to start there and it's easier to fasten it lower with a hose clamp. I used a spring binder up on top
as I could attach it with one hand that way without taking the fuel tank back off.
cvphoto4253.jpg
 
(quoted from post at 16:56:00 05/02/20) While technically true that a gravity feed system is hard to vapor lock because the bubbles just flow uphill to the tank.
It is also true that gasoline starts boiling (turning from a liquid to a gas) at temperatures below 100 degrees F.
This can disrupt gasoline flow to the point that a lay person calls it vapor lock.



Yes John...... I also.....still call it vapor lock... as the vaporized gasoline has blocked the fuel flow. Fuel pumps were added to stop the boiling of the gasoline as pressurized fuel has a higher boiling point and the fuel pump will push cool gas up the line to the carb on a hot day with a hot engine. So fuel pumps were added to most all vehicles and the fuel tank moved to the rear...

Alcohol in the fuel has reduced the boilling point even more???

Some call it toomalltoe,,, I call it vapor lock anytime you have vapor blocking the flow in a gas line. It was vapor lock before the fuel pumps were added and its vapor lock after the fuel pumps were added...
 
Well, sorry for not getting back to this with an update, everyone.
So, I loosened and then reset the sediment bowl to as absolutely close to vertical as I could get. It now rests just a hair off off the carburetor itself.

Since then, I've not had the hesitation/stalling problem. I find it difficult to believe that a rotation of no more than a couple of degrees would produce that result, but that seems to be the case and I'm willing to leave well enough alone (for now). I haven't seen the air gap / bubble since I rotated the bowl, either, FWIW.

Thanks for all the input, suggestions, and help!
 

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