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Problems vapor locking-the closepin theory

Discussion in 'The Hokey Ass Message Board' started by Chris, Apr 24, 2007.

  1. I started a thread a couple days ago asking if anyone had any recomondations on my 1941 Ford acting like it was running out of gas. It has a stock 59A flathead, and at high speeds or steep hills it would simply start bucking and pulsing, like it was running out of gas. It would even sometimes stall, and not want to start easily. A lot of suggestions were given, but until today after cleaning out the line, changing fuel filter, fuel pump, even trying another carb with no luck, I think I found my awnser. Vapor lock. When the car stalled out with the the second carb test run, I got out, pumped the throttle and saw no gas squirting down the barrells. "Out of gas"? No, it has over a half tank. I had a spare can in my trunk, so dumped some gas down the carb and it fired to life. I figured it was vaporlocking, thus making it act like it was running short on fuel. My friend suggested a theory he heard about sticking 5 or so wooden close pins on the metal line running from the fuel pump to the carb, the wood acting as a great heat dissapator. I did this, and took it for the same test run where it always stalled, but this time would scream down the road without missing a breat! The theory worked!

    Now my question: How can I prevent vapor lock without having to go to an ugly fuel cooler or somthing? Can I make my fuel line differently? Anyone ever have the same problem with a flathead V8?
  2. old beet
    Joined: Sep 25, 2002
    Posts: 5,750

    old beet

    Used to do that when I was a Kid..It works with a flathead and steel line! One guy used to put a half of grapefriut on his fuel pump, swore by it. Maybe you could insulate it and wrap with foil, but clothepins are cheap!!.....OLDBEET
  3. Thanks OLDBEET, just looking for a better looking more permanent solution ;)
  4. close pins act as heat sinks. ultimate cure is a electric fuel pump inline with a toggle switch. turn it on when you need it
    dan griffin likes this.

  5. 50dodge4x4
    Joined: Aug 7, 2004
    Posts: 3,535


    The problem is where the fuel line runs along the frame. Between the exhaust and the frame, the steel line gets hot and starts to boil the fuel inside the line. The cure would be to either reroute the fuel line away from the between the exhaust and the frame location, find a way to cool the line, or install an electric pump tp push the fuel to the carb or mechanical engine mounted fuel pump. Gene
  6. Not to sound stupid, but how would you cool the fuel? The car has a stock engine mounted pump.
    Another dumb question, if it is boiling clear down twards the rear of the car, why would the close pins (heat dissapators) work clear up at the carb? Wouldn't the fuel be cooled down by the time it gets all the way up front???
  7. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,406

    Flat Ernie
    Tech Editor

    Here's something to try - next time it "vapor locks", disconnect the fuel line at the pump & blow back into the tank. If you've got junk in your tank, it'll often slip-n-slide around & find it's way to your tank pickup starving the engine of gas.

    Vapor lock doesn't usually happen while you're driving because the fuel in the tank is cool & constantly cooling the lines & pump with fresh, cool gas. Vapor lock usually occurs when you stop, heat soak the bowl & pump, & then it doesn't want to start. That doesn't mean you can't vapor lock while running, just that it's not common.

    Most of these old cars have their original tanks with 50+ years worth of dirt, dust, rust, varnish, bugs, etc. in the tank - it's a small pickup tube.
    Joined: Jul 16, 2006
    Posts: 2,571


    And if the tank is not breathing properly, a suction will stop the fuel from getting to the carb. seen it happen.
  9. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,406

    Flat Ernie
    Tech Editor

    Good point, Bishop.

    Also, to touch base on the closepin - I view it more as insulation than cooling - helping to prevent heat soak. I've also seen crinkled up tinfoil used on the line from the pump to the carb...
  10. TRAVEZ
    Joined: Jan 21, 2005
    Posts: 584


    i am always in that similar situation every summer in my buick. i drive my car for a while. and then when i get in and start to go my fuel pumps starts pumping real loud and the car wants to die out. so i have to let the gas catch back up so it will idle alright. i tried the clothespin thing=no worky. i sitched out my mechanical pump to an electric pump and it still likes to stall out on me. over the winter i found out that it was my tank that gets clogged when i go under a half a tank. this summer i'm switching out my gas tank and hopefully this will remedy the problem.

  11. fuel pump
    Joined: Nov 4, 2001
    Posts: 3,620

    fuel pump
    Member Emeritus
    from Caro,MI

    By moving the fuel line are are not really cooling it you are getting it away from engine/exhaust heat. If you do re-route your fuel line be sure you always run it uphill. Any drop in the line will create a trap where vapor will stay until it cools enough to become liquid again. An electric pump mounted back by the tank is the best solution.
  12. rixrex
    Joined: Jun 25, 2006
    Posts: 1,433


    Driving around in a Texas summer, it can be 140 on the car was doing the same thing, I had used clothespins before but was looking for something more the fuel line away from anything hot and put a new Edelbrock onnit..I know thats not everyones fix, but it solved a variety of problems, vapor lock,choke,idling,performance etc......
  13. 1950ChevySuburban
    Joined: Dec 20, 2006
    Posts: 6,188

    Member Emeritus
    from Tucson AZ

    Since wood is a poor conductor of heat, they shouldn't work. Thats why BBQ pits have wooden lid handles. Unless your using metal clothespins.
    belair likes this.
  14. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Don't discuss vapor lock til you've done some diagnosis.
    2 dirt simple free tests: Run engine in driveway, turn off, drain carb from one of the big plugs in front into measuring cup. There's how much gas should be in bowl...and if car will restart in a few spins, obviously pump is OK in the driveway.
    Run car til problem happens, switch off, clutch in, coast off road. Drain carb...less fuel there or not??
    If carb is low, put fuel line from pump to carb into a container (and think carefully about how not to spill any flammables), crank engine with ignition off and see if pump pumps. If no pumpage, we start diagnostcs on pump and line system...
    vapor lock is simply a wild guess at a problem that could be almost anything at this point.
  15. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208


    I had a similar problem in my 47. For my case it wasn't vapor lock it was a randomly plugged fuel line - with the problem being some "muck" in the tank. The truck sat for many years before I got it. After driving it for a month or so it seems that the "coating" (varnish??) on the inside of the tank was flaking off. This eventually plugged the fuel filter.. I replaced the fuel filter and it happened again except this time the filter wasn't plugged. As it turned out the large flakes of muck would slide around in the tank until they covered the opening. If I slowed down the truck would run better - but going down the road it would die. I'd crank it and it'd start right up (didn't need much flow to get it to idle) but go down the raod and it'd die again.

    The tank in my truck has a fitting on the very bottom - so the muck would slide around until it plugged it up (at varying degrees) which made it kinda fun to diagnose. When I finally figured all this out - I removed the tank and pressure washed it - not a single spec of rust - just this "flakey" muck that woudl crumble like dust when dry. It's one of the first things I'd check if I were you.
  16. Thanks guys,
    The tank was professionally cleaned, and I even removed the sending unit and peeked in it and it looks brand new inside...NOT SAYING THAT COULD NOT BE THE Bruce said it could be anything right now. I'm just trying to eliminate possible problems. I am going to try a new, vented cap, as I never thought of that :) It's just funny how it ALWAYS did it, and as soon as I put those wood close pins on it runs fine....maybe a coincidence!!! My luck!!!
    Thanks all, Chris
  17. pasadenahotrod
    Joined: Feb 13, 2007
    Posts: 11,776

    from Texas

    The problem may also be the flex fuel line that mounts from the fuel line at the firewall to the fuel pump. If the line is old (that means if you haven't replaced it) it can deteriorate inside like a brake hose and the fuel pump can suck it shut or a piece of hose flop down and block the line.

    Any old car should have the hoses, belts, fuel flex line, brake flex lines(2 front and 1 rear) checked and likely replaced when you get the car unless it has obviously been done.
  18. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Eliminate or incriminate the fuel system by checks above...cap issue can be resolved by a short run with no cap. Flex line is indeed a trouble spot...
  19. 49willard
    Joined: Nov 2, 2006
    Posts: 93

    from Maine

    I agree with the clothes pin fix btdt. Driving cross country late june in the late 70's with my 322 nailhead powered 49 F-1 flat towing a Model A Vicky the clothes pin fix got me home. I did not believe that it would make a difference but it did. The clothespins were wood, given to me by an older gent in Nebraska. I took his address and sent him a fresh supply after arriving on the east coast. I think that the pins clamped on the line create additional turbulance in the airflow around the fuel line rather than conduction of heat away. I also had the grapefuit fix suggested back then however wrapping the stock fuel pump with a wet cloth contained with a split coke can was not enough. The clothpins alone did the trick
  20. pan-dragger
    Joined: Sep 13, 2006
    Posts: 3,187


    clothes pins and tin foil never worked for me.. i istalled an inline fuel pump and my vapor lock problems were over..
  21. OK, so not to beat a dead horse...BUT...I installed a different distributor today (I had a Mallory and went to orriginl Crab) and the problem is still there, so it is not an ignition problem. This time it did it driving home from my Dads, flat road about 35-40 MPH. It starts bucking and stalling, and if I left off the gas it will idel just fine, but if I give it any throttle it dies and will not start. Now, heres the weird part. If I pour a little gas in the carb (maybe 1-2 minutes after it dies and will not start) it fires right up and runs fine. Is this still vapor lock???? I will install an electric pump if thats what it takes, but I am not really sure thats my problem. Suggestions, guidence? My club is going on a 200 plus mile cruise this weekend and I really want to go, but as un-trustworthy as the old 41 is, I do not want to risk it. UNLESS I can get this little problem figured out.
    Either way, enough rambling. Suggestions? Comments?
  22. fuel pump
    Joined: Nov 4, 2001
    Posts: 3,620

    fuel pump
    Member Emeritus
    from Caro,MI

    If it runs by pouring LIQUID gas into the carb then you have vapor lock. Bottom line the gas is turning to vapor before it gets to the carb. An electric pump mounted down low back by the tank will pressurize the fuel line and may stop the gas from vaporizing. A last resort is to give the vapor somewhere to go rather than into the carb! You can do that by installing a fuel/vapor return line. Basically you put a T fitting with a small (0.060") opening (pointed up) in the fuel line near the carb and run it back into the tank. When the vapor gets to the T fitting it purges out and returns to the tank. Another advantage of this system is it circulates the fuel which helps keep it cool thus preventing vapor. Good luck.
    Joined: Nov 13, 2002
    Posts: 1,229


    I had to replace my coil,seems it quit working when it got hot!
  24. Dirty2
    Joined: Jun 13, 2004
    Posts: 8,903


    Have you checked to make shure there is nothing in the tank that is blocking the fuel outlet ?
  25. I had this problem in my fifty three Buick. We insulated the line from heat, rerouted away from the exhaust, and flushed the gas tank. After all that it never did it again. Good luck, Rags
    Bruce Fischer likes this.
  26. countrytravler
    Joined: Oct 27, 2012
    Posts: 161


    BUMP, That time of year coming on!!!
  27. Good idea. Lots of new young members who will run into the same problem.
    Noticed the first reply here was from OldBeet, last seen here 5 years ago. Where did he go ?
  28. kma4444
    Joined: Sep 24, 2008
    Posts: 197


    IMO the liquor doctored fuels we are usually stuck running now are more prone to boiling under heat and vacuum conditions. I would add an electric pump at the tank, a quiet one, and be done with it.
  29. I second that. Helper pump. Never have another problem, also fills your bowls after car sits.
  30. tjc1965
    Joined: Dec 13, 2012
    Posts: 1


    Very timely for me. I've been lurking a while, finally have a situation I need some help with.

    My Dad and I have a 1951 Ford Tudor we bought a couple years ago, mostly restored to original, but a few little things needed, something he can putter on and take to cruise nights.

    Always starts and runs good, but I think have messed something up this weekend. Previous owner installed a Mr. gasket inline fuel pump many years ago. Pump mounted to the frame rail, basically under the drivers door. The pump is wired to only get power when the starter is cranking- hot wire right on the outlet from the solenoid. So I figure the pump is used to get the fuel flowing at start-up, and then the mechanical pump takes over.

    Today I replaced the pump and filter, since the old pump had a slow leak. Bought a Carter electric, similar size as the old one, low pressure type. Wired it same as the old one - runs only when on the starter.

    After installing, went for a ride. After about a mile, she stalls. Coast to the side, wait less than a minute, starts right up. Drive another half mile, does it again. So, we turn around head for home does it again a couple times.

    Once home, decide to see if it's "vapor lock" due to heat. Let it idle in the driveway, hood closed for 20 minutes or so figuring it might make enough heat to boil the carb fuel. No dice.

    However, with my foot on the pedal and holding it at 2000-2500 rpm, in about a minute she sputters and shuts off. 30 seconds, starts right up.

    So, my theory now is the new pump is more of a restriction in the fuel line than the old one, causing the mechanical pump to lose prime. Any one have any thoughts on that?

    For a solution, I think if I just run the new pump off the ignition hot wire, so it's running whenever the key is on, that should solve the problem. Only question now, do I need a regulator before the mechanical pump to not over-pressurize it, or not to worry?

    Thanks for the help!

    Tom C

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