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Technical I'm still fighting vapor lock.

Discussion in 'The Hokey Ass Message Board' started by NAES, Jun 28, 2020.

  1. NAES
    Joined: Dec 24, 2008
    Posts: 484


    I posted almost a year ago trying to track down a poor running condition, overheating and fuel starvation problems.

    I redid the entire cooling system with a new radiator and electric fan. I used the evaporust coolant system cleaner with great results but was still getting what I am assuming is vapor lock.

    After being disheatened for a while from not solving the issue I'm back on the horse. I suspect I'm getting vapor lock due to the routing of my metal fuel line from the pump to the carb. It hugs the block pretty well and is definitely getting some radiant heat. I was getting up to 160* on the metal line using an infrared scanner. The pump runs 3.5-4 lbs using an inline gauge.

    Here are my thoughts. I am totally open to any and all suggestions. I added a few pics of my fuel line route.

    1) Replace and reroute the line from the pump to the carb with rubber fuel line further away from the engine block.

    2) Use some type of heat shield and/or fuel line wrap.

    3) Add an electric pump and either run it in line with the mechanical pump or replace the mechanical all together.

    4) Add a return line to the tank to pump warmed fuel back and keep cool fuel flowing. I think there was an AMC fuel filter that has a return nipple or run one off of the carb (Edelbrock). This is my least favorite option.

    My wagon once was my daily driver for over a year and also the car I could always rely on to just jump in and go anywhere. I think the added alcohol in the fuel has really played a role in my vapor lock issue. My confidence in it is shaken and it really has put a damper on enjoying it.

    Thanks everyone for the help, NAES. 20200627_165853.jpeg 20200627_165840.jpeg 20200627_165836.jpeg

    Sent from my SM-N950U using The H.A.M.B. mobile app
    Elcohaulic likes this.
  2. anthony myrick
    Joined: Sep 4, 2009
    Posts: 7,446

    anthony myrick

    following, mine will do that on super hot days. Ethanol boils at a lower temp non ethanol.
    I plan on adding a carb insulator. if that doesn't help then a return line or reroute the line from the pump or insulate it
    anothercarguy likes this.
  3. Looks tight in there, but still pretty standard routing. I would remove the fuel line, add some hose barbs and rubber fuel line with a clear unbreakable filter and see what happens. A weak coil or condenser could also cause the "hot start" issue...
    Last edited: Jun 28, 2020
  4. NAES
    Joined: Dec 24, 2008
    Posts: 484


    I forgot to add that I did install a phenolic spacer as well. Didn't help. Thanks for the reminder.

    I'm willing to put in the work. Just wanting to hear others opinions about what all to do.

    Sent from my SM-N950U using The H.A.M.B. mobile app

  5. spanners
    Joined: Feb 24, 2009
    Posts: 1,150


    I ran a return line back to the tank. My fuel line was 5/16 from the tank so I put a 't' after the mechanical pump and ran 1/4" back to the tank. Shittiest bit was soldering in a fitting into the tank but it was better than sitting at the 'lights with a stalled engine and getting abused.
    I was told to use the smaller diameter return line as it allows enough pressure to the carb when needed but the pump still circulates the fuel.
    King ford likes this.
  6. rtp
    Joined: Aug 14, 2007
    Posts: 174


    I will try it help. First ,what car ,what engine,? When does it happen ,after a few minutes or miles?
    Where you are looking is after the pump , this is under pressure. Can't see fuel boiling there . I would look between the tank and pump . that line is under lower pressure or vacuum. Easier to boil the fuel in a vacum. That's what vapor lock is . your pump can't pump vapor. And any gravity feed from the tank is not strong enough to push it to the pump.
    Electric pump at tank could fix it.
    If there is any rubber hose between tank and pump it could be sucking air if cracked.
    I would check all the lines for seeping fuel or rust ,and for any place they are close to heat.
    The again I had what I thought was vapor lock happing on my car chased that 6 months then the hei module died . changed that and no more. Vapor lock symptoms.

    Sent from my VS987 using The H.A.M.B. mobile app
    belair, ClayMart and pitman like this.
  7. 51504bat
    Joined: May 22, 2010
    Posts: 2,675


    On the 8ba flathead in my '39 p/u I installed an electric fuel pump back by the tank in addition to the factory mechanical pump. Its wired with a toggle switch that I flip when needed. I use it mainly to prime the carb after the truck has been sitting for a while but its nice to have in case of vapor lock.
    pprather and alanp561 like this.
  8. flamedabone
    Joined: Aug 3, 2001
    Posts: 4,907


    I had the same issue. My fan was blowing hot air right on the fuel pump. I made a heat shield and wrapped the pump in heat shield material.

    Also wrapped the fuel line from tank to regulator in heat shield material. Completely cured the problem.


    AHotRod, malibro and alanp561 like this.
  9. NAES
    Joined: Dec 24, 2008
    Posts: 484


    Thanks guys for the excellent info so far!

    Car is a '53 Chrysler Town and Country wagon. Mopar 360 engine/727 auto trans. Aluminum radiator, electric fan, 180* switch.

    The HEI is a generic unit I've run for about 10 years so it may be well worth looking into. Thanks for that tip.

    Symptoms start after 10 minutes or so of running. Engine gets warm, fan comes on and at cruise speed all is well. Off throttle it stumbles requiring me to blip the throttle and hold brake and gas at the same time while stopped or throw it in neutral and keep the revs up around 2000 or so. If I let off the throttle it dies and takes a good 10 minutes to restart it. Then I still have to keep the revs up or it will stall again.

    Fuel line is steel from the tank to the rear axle, rubber fuel line and filter up and over the rear frame arch then back to steel line up to 6" from the fuel pump where a rubber line connects the 2. After the pump its all steel to the carb. All rubber line is new and filter is new as of a year ago when I was chasing this issue before.

    Many many thanks, NAES

    Sent from my SM-N950U using The H.A.M.B. mobile app
  10. Fixed mine! OT, though. No "vapor lock" for past ten years, 20,000 mi.

  11. NAES
    Joined: Dec 24, 2008
    Posts: 484


    How you fixed it would be very helpful! Lol

    Sent from my SM-N950U using The H.A.M.B. mobile app
    Cosmo49 and clem like this.
  12. birdman1
    Joined: Dec 6, 2012
    Posts: 1,157


    In the late 80's, I was working in a Ford dealership. On the van, ford made a metal heat plate shield that was placed between the carb and manifold. They also had a fuel bypass valve assembly that went in the fuel line just before the carb. It allows fuel to be circulated back to the tank. It did help
    Kevin Ardinger likes this.
  13. pitman
    Joined: May 14, 2006
    Posts: 5,041


    Clever, insulating or upping flow, on the pump suction side.
  14. Electric pump, bypass the mechanical, run the line away from heat as much as possible. Use hose from the frame connection to the carb, check the float level in the carb. If it's low, it will aggravate the problem.
  15. cheepsk8
    Joined: Sep 5, 2011
    Posts: 562

    from west ky

    I fought it in an off topic K10 pickup for about six months. Started during hot weather so naturally, I figured heat on my metal fuel line. So to rule that out, I went in the house and robbed some aluminum foil and wrapped it good. Problem went away for a while, then one warm day in the fall, here we go again. Turns out my diapragm in my fuel pump was dying a slow death. Put a new fuel pump on and drove for years with no more issues.
  16. whateverit takes
    Joined: Sep 5, 2013
    Posts: 58

    whateverit takes
    from Florida

    I went through a fuel delivery problem that at one point I suspected vapor lock. I performed all the usual remedies, blowing the line, rebuilding the carb, replacing the tank, insulating the metal line near the engine, etc. After 3 "new" mechanical pumps (2 Airtex and 1 Carter) failed to correct the problem, I sectioned the frame to allow a high volume AC Delco pump to fit. This solved my issue. The moral here is don't trust a new or relatively new mechanical pump. Put a pressure gauge on and/or a transparent fuel filter so when it occurs you can stop and see what you're dealing with. I was getting 4 - 5psi with the "new pumps but not enough volume to maintain a steady flow. I could see the fuel pump pulses through the nearly empty filter. I also run an electric pump new the tank as a precaution.
    loudbang likes this.
  17. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,230

    from illinois

    If you can't keep it running at idle , that sounds like a vacuum leak ?
  18. Screenshot_20200628-123214_Google.jpeg

    this will cure it permanently.
    I have been using it on my Studes since the late 80s
    They used to vapor lock a whole lot in warm weather.
    Now they havent in years :)
    you need to keep the fuel moving or it will soak heat and boil

  19. leon bee
    Joined: Mar 15, 2017
    Posts: 566

    leon bee
    from Arkansas!

    That's Ole Ben, he ain't supposed to mention how he solved it.
  20. anthony myrick
    Joined: Sep 4, 2009
    Posts: 7,446

    anthony myrick

    setting up the fuel system on my kids 61, building the pick up tube for the tank, you folks convinced me on adding a return line.
    going to try the filter return.
    King ford and pitman like this.
  21. Agree with 51504bat in post 7. Rarely need the electric pump but occasionally it helps overcome a vapor lock on the highway. Also use it to prime the carb when rod not started for more than a few days.

  22. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,330


    I'm betting your issue is happening before the fuel pump. Where the steel line between the tank and the pump runs makes a huge difference. If that line runs in a place where heat from the exhaust can get trapped around the fuel line, you get vapor lock. Running the steel in a way that avoids the line from being in an area heat can get trapped may solve your issue.

    An electric pump at the tank would probably solve your issue as well, but you may need to run a return line and a pressure regulator.

    Just adding a return line to the fuel system may solve the issue as well, but all my stuff has an electric pump at the tank. Gene
  23. rockable
    Joined: Dec 21, 2009
    Posts: 3,350


    I had the same problem with my 57 Chevy. I took a length of 3/8" fuel hose I had lying around and split it. Then I put it over the metal fuel line from the pump back past the header. This insulated the metal line sufficiently to stop the problem, so far. If it continues to work ok through the hot part of the summer, I will either route hose to the pump or re-route the hard line. The boiling point of fuel these days is absurdly low for traditional fuel systems and carburetor. I have taken the top off of my Edelbrock carb on a heat soaked engine and witnessed the fuel boiling. Lowering the pressure (inlet side of the pump) only makes the boiling point go lower.
  24. Not supposed to talk about that. The initials ar F.I.

    leon bee likes this.
  25. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 909


    I use an ON-TOPIC fuel filter that has a return line. It's first use was in the 1963 Buick Riviera and soon found it's way into lots of AMC, GM and Jeep vehicles.

    Picture credit: Summit Racing.

    WIX 33040, Microgard 33040 and probably some other cross-references. 5/16" in and out, 1/4" return.

    The return was routed to the filler pipe on my fuel tank. The filler pipe was removed to install a 1/4" hose bib. Due to the heavy zinc plating, J-B weld was used.

    The return flow was a steady, small trickle.

    Some other tricks:
    1. Aftermarket plastic spacer under the carb.
    2. Home made 1/8" aluminum heat shield between the spacer and the carb. Custom cut for maximum coverage.
    3. Home made cold air kit using a modified air cleaner off of a junk pile (Filter crosses to mid 1950's Mopar)
    4. Lots of silvered fabric pipe insulation (Source Reilly's) on the fuel line - Both in the engine compartment and in the rear axle area.
    5. Header wrap on the header (singular - it's a banger) and all the exhaust pipe that I could reach all the way to the back. Exhaust system passes near the fuel tank (stock location - no reasonable alternative routing).
    6. And several items that will get this thread deleted <sigh>

    A couple of weeks ago, on a 100 Degree F day, I pulled a mile long hill (I-10, Benson, AZ). 74 MPH, on the cruise control, AC blowing cold air. No sign of fuel starvation (monitored with an Air/Fuel Ratio gauge).
  26. I had serious vapor lock just like you are describing. It would leave me stranded at a red light for 10 minutes blocking traffic. Tried different mechanical pumps, carb spacers, etc. I tried your #1, your #2, (already had #4, didn’t help). #3 solved it, electric helper pump just after tank, on a toggle, in line with mechanical pump. Not one issue after that. Works flawlessly, also primes carbs so engine fires right up every time, (float bowls would basically evaporate overnight before the electric pump). I’m never going back.

    Mine was a 100% stock system (Cadillac 390) that probably worked flawlessly up until 10% ethanol content.

    Sent from my iPhone using The H.A.M.B. mobile app
    Last edited: Jun 29, 2020
    pprather likes this.
  27. ramblin dan
    Joined: Apr 16, 2018
    Posts: 2,481

    ramblin dan

    My buddy had a 57 Chevy that had same problem and he put in a carb spacer and that seemed to do the trick.
  28. NAES
    Joined: Dec 24, 2008
    Posts: 484


    Man you guys thank you so much for the help! I really feel re-energized and ready to tackle this problem again.

    Also, thank you to those who sent me PMs and emails with thorough and detailed breakdowns of what to look at and what to try.

    I'll update this thread as I make progress.

    Seriously, you guys are all fantastic! NAES

    Sent from my SM-N950U using The H.A.M.B. mobile app
    pitman likes this.
  29. jimmy six
    Joined: Mar 21, 2006
    Posts: 8,796

    jimmy six

    NAES, maybe it’s just dumb luck but my cars fuel line from the tank is on the outside of the left frame rail with the brake line. My under hood line is all steel and about the same distance away from the block as yours. I too have a space but it’s phenolic not plastic. I checked yesterday day with my temp gun while looking to a trans leak and it was at 120 on the steel line leading to the carb. My pressure is 4-1/2 to both carbs and I have an AC glass type filter after the pump before my tee to the carbs and I always see fuel in it.
    This may have nothing to do with it but I have always ran a fuel additive with today’s gasoline’s. 8 years. Started with Bright Star, then Stabil now Stabil Marine and I have never had your problem and I too live in So Cal. Good Luck
  30. carbking
    Joined: Dec 20, 2008
    Posts: 3,008


    Late to this thread.

    Would suggest the following:

    (1) Reroute the line from the pump to the carb so it is in open air. Custom bend a steel line.
    (2) Replace ALL neopreme lines EXCEPT the "vibration" link from the line at the frame to the fuel pump with metal line.

    Try the above. If replacing the line from the pump to the carb doesn't solve the issue; then: add one of the 3 line filters as pictured by others in this thread RIGHT AT THE CARBURETOR. Run a new metal line from the "vapor return" port on the filter all the way back to dump into the top of the tank.

    If that does not solve the issue, then look at this link BEFORE doing an electric pump:

    And make certain your coil is not breaking down with heat! A coil breaking down will exhibit the same symptoms you posted.


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