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Vapor lock quick fix???

Discussion in 'The Hokey Ass Message Board' started by speedo, Apr 8, 2005.

  1. speedo
    Joined: Jul 4, 2001
    Posts: 74

    from Dayton,OH

    I have a 66 Caddy at the shop, complaint is that when it gets hot, the fuel is cutting out, fuel box is empty. After about 10 minutes or so, it fires up again and the bowl is full. I checked the main line into the pump, from the tank and it was cracked and I replaced it.....

    Now here's the problem, it doesn't die now, but you can tell that it is still running out of or low on fuel. I just replaced the pump, last summer, due to a service manager that thinks that's the problem, and wants me to do it again. I hate to charge the guy for a pump again. I can't see how a pump would shut down when it's hot, they just don't do that. A mechanicla pump, is just that, it either works or it doesn't........

    It has the symptoms of vapor lock, it sounds like. Just not sure if there's a quick and dirty way to check.

    Anybody run into this?
  2. J.D.
    Joined: Oct 1, 2004
    Posts: 788


    My '64 Lincoln did it right after I replaced the fuel pump (wans't running before hand) I just ran a electric pump in line back at the tank so when it started cutting out I just click it on and go on my way (kills the gas milage when it's on). I always just figured my fuel lines had some build up in them or something not letting the fuel flow properly. Good Luck
  3. 4woody
    Joined: Sep 4, 2002
    Posts: 2,010


    Wrap the fuel line near the engine and exhaust with Thermo Tec or similiar heat shield. If it is vapor lock it'll make a noticable difference.
    59Apachegail likes this.
  4. stealthcruiser
    Joined: Dec 24, 2002
    Posts: 3,668


    make sure the gas cap is good and will relieve pressure and vacuum.
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  5. check the entire line for leaks/splits as that would do same thing..also the problem could be in the tank at the pickup tube/sock /screen?

    I have taken tanks apart and cleaned em and the tube was clogged with rusty plaque type substance- very hard to clean out too.......
  6. 61bone
    Joined: Feb 12, 2005
    Posts: 890


    Vapor lock doesn't happen between the pump and the carb, it happens between the tank and the pump. The suction of the pump lowers the pressure in the line and a t the same time lowers the evaporation point of the fuel. So if you have a restriction or a hot spot in the line the fuel evaporates before it gets to the pump. The pump won't pump enough vapors to run the engine.
    So check for areas where the line runs close to the exhaust system or lays downstream of heat from the exhaust. Best way: drive it till it falters, crawl underneath and run your hand down the fuel line feeling for hot spots. They'll be easy to find.
    Check for restrictions: smashed lines, plugged lines, plugged pickup filters and the most insidious of them all the deteriorated rubber line on top of the tank.
    Get the flow specs for your car and check the fuel pump output cold. If it's not to spec see above before you replace the pump. While a new pump may cure the problem it is likely due to other causes and will recur if the pump you have is fairly new and will pump to spec from a container that eliminates the present fuel system. Disable the ignition. Take your emergency fuel supply can and a short piece of the proper size hose and hook to the inlet side of the pump. Another piece of hose on outlet into a graduated container. Crank for specified time and measure output
    If the pump fails both tests replace it. If not, the problem is one of the above.
    happy cruzin
  7. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    I encounter vapor lock situation after crawling in traffic for 45 min engine temp was hovering at 220 I got out of the traffic jam and started moving and engine acted as if it was running out of fuel. I pulled over to inspect things and the engine died and wouldn't restart for 2 hours. called roadside assistance and got towed home and of course it started right up and ran for an hour . then it started sputtering again I felt the pump on the frame and it was warm but not hot enough to vapourize fuel. I looked at my fuel filter and it was empty (clear filter) checked electric pump output and it was 10 psi, before regulator and 5 psi at lines to carbs, so my pump is working . there is presently no return line in my system and I suspect the Glass fuel filter is vaporizing the fuel and no return as the cause . the fuel line with filter by alternator was to close to the cylinder head, filter was empty and smoking hot to touch . I removed the glass filter, rerouted the fuel line away from the block. drained out the 94 octane fuel and refilled with 87 and then drove the same route . so far No more issues altho it really isn't that hot here in Canada yet (14 degrees). I have a new fuel cell that has the return and vent built into it so I will be changing this before the weather gets to warm. I definitely would rather be cruzing then waiting to get towed home. This new fuel smells awe full, nasty stuff in it. it is not he same fuel we were being sold even 5 years ago. I am hoping that a fuel cell with a return line will help cool the fuel, anyone had issues with a fuel vapor lock in a system with no return line? getting towed home is no fun .
    Last edited: Apr 12, 2017
  8. When I was a teenager the common cure was wooden cloths pins line up and down the metal fuel line. HRP

    bedwards likes this.
  9. Clothes pins - yea a bunch of times. Wrapped the line in aluminum foil. Moved the fuel line from in front of the block to around the head with a new fuel line, ice on the manifold.
    This was done with an OT old motorhome with a 454 motor. And it was finally fixed (after two terrible trips to Bonneville and a new $2000 radiator in Vegas, I almost was killed by the wife) and it was the brand new fuel pump. A $40 pump change and I was running down the road.. it would stop running when it got hot from the road and from sitting and idling.
  10. Clothes pins got our 48 Chrysler between Needles and Flagstaff every time Dad took us to visit the Grandparents in Missouri.
  11. porknbeaner
    Joined: Sep 12, 2003
    Posts: 38,755


    I don't know your system or your engine or pump. Some pumps do not require a return line, they have enough clearance in the body that it is not an issue. The higher volume pumps do require a return line and they should be running a by-pass regulator. The regulator on any system should be located as close to the carburetor as possible, there should be no filter between the regulator and the carb.

    None of this is give as a cause or solution to your problem it is just the most commonly accepted way to properly set up a fuel delivery system.
  12. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    cool thanks for the info. my engine is a 1958 283 bored 30 over all rebuilt ,I have a round tank from a straight truck with one fitting, runs to a filter, to the pump (via rubber hose) down the frame with 3/8 rubber hose, to another filter, to the regulator on front right frame rail to the fuel log that feeds 4 - 2 barrel carter carbs. I removed the glass filter that was after the regulator as the glass was really hot and filter was empty when this vapor lock occurred ,engine was hovering at 190-200 in traffic once I got moving a bit it cooled down to 180 then stalled out and wouldn't stay running like it was starving for fuel, I figured it was a bad idea to have glass filter close to the block that is good at attracting heat so its gone and line has been re routed . pump is good it is pushing a consistent 10 psi to the regulator and 5 at the log . I was thinking maybe changing the line to steel from the tank to the regulator. but not sure if steel line will help to keep fuel cool or make the problem worse? what do you think? rubber or steel? do I need carb spacers? may have just been that glass filter...... it was empty when I flicked it with my fingers the fuel slowly refilled the filter and the engine started right up.
    Last edited: Apr 12, 2017
  13. clunker
    Joined: Feb 23, 2011
    Posts: 1,419

    from Boston MA

    I have a '60 Cad. It always had vapor lock issues (for the 16 years I've owned it anyway). Tried changing fuel pumps, replacing entire fuel lines, (return line too), tried insulating any line that was accessible. Tried restricting return line. After years of car dying wherever it felt like it, (always started after 20 min), I installed an electric helper pump just after the gas tank, in addition to the mechanical fuel pump. Never happened again. I didn't really like the idea of an electric fuel pump, I like to make the old tech work, but I just think these systems were not ever going to use ethanol well.
  14. porknbeaner
    Joined: Sep 12, 2003
    Posts: 38,755


    Long runs of rubber line are not a good idea. better off to hard line it from the pump to the regulator. Even if you use a littler nipple to connect from the hard line to the pump and regulator on both ends.

    One of the problems that we have is that our old mechanical pumps have rubber diaphragms and the rubber does not like the ethanol real well. If it were mine and I was going to run a mechanical I would only run the electric when I was having a problem and not run it all the time. It never really was a problem with the old pulse pumps but I have seen more positive pumps over ride a mechanical more then once.
  15. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    I am only running 1 Holley 10 psi electric pump. only using 5 psi at the carbs its definitely heat related. I do not have these issues if I don't get stuck in traffic which is almost impossible with the weather getting nicer, and the dreaded construction season starting here in the city. so using rubber is not a good idea? wouldn't take much to switch it over to steel I already have the roll of line and fittings. what about the lines to the carbs? I have 4 carbs all fed by rubber hoses I was thinking about making all steel lines but concerned about the heat in the center of the intake boiling the fuel . is the steel better at transferring/dissipating heat then the rubber? I don't want to put the steel lines on everywhere if it is going to trap more heat.
    Last edited: Apr 12, 2017
  16. deathrowdave
    Joined: May 27, 2014
    Posts: 597

    from NKy

    Older pumps had a super small orifice between , inlet and outlet side to allow a small amount of flow all the time . This also relieved pressure when shut down , to stop flooding of the carb inlet seat and hard hot starts . This is gone once the "crimped" Non rebuildable pumps arrived . You can you an inline filter with a 3 lines , on is a return to the tank to supply constant flow , just something to think about .

    Sent from my iPhone using The H.A.M.B. mobile app
  17. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    I have a brand new Jaz fuel cell 15 gallon with anti slosh foam , I will be installing it on the weekend it has a return built into it as well as a roll over vent valve should cure the problem with the fuel getting to hot. running steel lines from the pump to the regulator seems a good idea as well . the current tank doesn't have a bung (fitting) for a return line. and I am not running a mechanical pump. only an electric. altho if these electric pumps keep leaving me waiting for a tow truck it will have a mechanical pump very shortly ! LOL. I have Never had this issue with a mechanical pump. but every car I have ever owned with an electric pump had to be replaced sooner or later because it failed . hopefully the changes we make this weekend cure this . the pump is working its new and has been tested.
  18. The Shift Wizard
    Joined: Jan 10, 2017
    Posts: 480

    The Shift Wizard

    Wow! A 12 year old thread back from the dead. :confused:
    I have a bouquet of short stories to add to the pile. I'm not an expert. I've just seen some things so just eat the meat and throw away the bones that you might find.

    Years ago in the early 60's, I had an acquaintance who had dressed up his engine compartment with a length of clear, red tinted, plastic fuel hose. With the car warmed up, you could open the hood and watch the vapor bubbles forming inside the hose. None by the firewall, then very small after a few inches, then bigger than a bb shot about half way down the block, then the size of peas and then big, caterpillar size bubbles making up half the flow by the time the hose made the turn to the pump. It was pushing more vapor than liquid fuel at the pump and who knows what was happening in the carb bowl. I suspect that when you "soup up" an engine past stock, you are also producing more heat under the hood with the increased power. Then if you factor in any changes to the body work, fan shrouds, inner fenders and shields, anything that disturbs the purging of hot air from the engine compartment, you may have double trouble with excessive heat issues.

    Fast forward to the 80's and there I am putting a ground effects, air dam on this car of mine. The fuel percolated so bad, the car bucked like a rodeo bull unless I cracked the hood a bit to scoop more cool air. My ex helped me with that problem by knocking the air dam off on a parking curb. It ran like a Swiss watch without the dam.

    Back to the late 60's....... At the drag strip we worried about "heat" a lot. My fuel line in the engine compartment was copper tubing formed into a many layered coil that was inside a gallon bucket type container that I filled with ice. The belief was that colder fuel was more dense even in the micro droplet stage in the intake mani. But if that wasn't entirely true, at least it didn't percolate. :cool:
  19. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    I would understand heat building up under the hood and causing fuel problems however I don't have a hood, my engine is wide open (see avatar pic ) with a huge electric spal fan to cool it off. Im sure most of this problem was the glass fuel filter to close to the head and having no return line to help keep the fuel moving. as well as rubber line for the entire length of the car. new tank and new steel lines going on this weekend. pump is new and working fine.
    Last edited: Apr 13, 2017
  20. 4decue
    Joined: Mar 15, 2017
    Posts: 12


    after changing the fuel line from the tank from rubber to steel, re positioning the feed line to the carbs away from heat, installing a new fuel cell with a return line the problem appears to be solved. So Far no more Vapor lock when stuck in moderate to heavy traffic . the true test will be when the weather is at its hottest and being stuck in traffic. but for now its all good . :D
    clunker likes this.

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