Vapor Lock On A Beautiful NW Summer Day

Slant 6 Engines

  1. Duggie

    Duggie Well-Known Member

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    First trip today over 5 miles since we purchased the Dart. Post head rebuild, new rod and main bearings, rear main seal, tranny overhaul, resurface flywheel and new clutch, new radiator. After 40 minutes on the highway, the \6 starts to surge and looses power. Let it sit on the side of the highway for 10 minutes and it's surging along again, dyeing at intersections. At the 45 mile turn around, I figure its vapor lock. How to get home? Wrap a water soaked rag around the fuel line and tie a little aluminum foil between the wet rag and manifold. Flashback to being 16 again. Glad I did this with my brother instead of my wife! HA!!
    vape.JPG
     
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    • pishta

      pishta I know I'm right....

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      Get' er home! Been there......got back to base once with a boot band (elastic band) as a carb return spring. Also drove a Subaru about 30 miles home without a clutch. Just time the lights......and hope your starter holds up for the times you have to stop.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      1...Very first thing is to make absoluty certain that tank is venting

      2...Second thing is to find a service manual --which you can download, free, from MyMopar--and read the section on fuel pump testing

      3...Do basic troubleshooting, IE make sure no lines are crimped, hoses rotten or collapsing, or filter plugged. Do not discount it could be the filter sock in the tank

      3....Look around, somewhere over at Slant six.org is an article on fuel line modification

      4....Best thing I did for my 67 although it is a V8--was convert to rear mount electric pump. This raises pressure in the fuel line which is normally under suction, and raised the boiling point----I built a return system using Wix 33040 series filter which has a built in return orifice, and use a thick insulator carb gasket
       
    • Michael Brisebois

      Michael Brisebois FABO Gold Member FABO Gold Member

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      I don't know if this helps, but it cost you nothing...and sometimes you "get what you paid for".
      An old friend (Corvette guy) offered to look at my 66 Coronet, that was having a similar sounding issue. His conclusion was that the fuel was boiling, or close to boiling in the carb. Today's unleaded fuel has a lower boiling point, so I'm told...about 185 degrees. While he tweaked a few a few other things, he said that the most dramatic change came from the thermal insulating spacer that was added between the carburetor and manifold.

      Good luck
       
    • Treblig

      Treblig Well-Known Member

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      How close to "any" exhaust pipe/header does your fuel line run? Is the fuel line properly suspended from the engine to prevent heat soak?
       
    • slantsixdan

      slantsixdan =..=

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      • Duggie

        Duggie Well-Known Member

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        You know Dan, I was thinking about when I read your article on this last spring. I was still looking for the right Dart to buy and thought to myself, "Self, you will probably never experience this in the Pacific Northwest." Proof again I'm the most dangerous when I think! HA!!

        I did think the mod was more complicated than it actually is, for some reason.
         
        Last edited: Sep 7, 2020
      • Duggie

        Duggie Well-Known Member

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        Oh you bring back memories! Drove more than one VW with a broken clutch cable, grinding on the starter at the green light. Got a buddy that drove out of the desert on the battery, with the elastic from his underwear around the crank and water pump pulleys. Oh and New Years Day in Weed CA, the local NAPA farm store owner opened up to cross reference wheel bearing numbers and sold me the bearings, grease, and tools to replace the bearings. I backed the car off a chunk of firewood when I was done and finished my 1100 mile cross country trip. My father in law rigged a string from the carb, in through the wing window so my sister in law could get home one winter.

        Geeze, this could be a thread all by itself couldn't it?
         
      • Naplm00

        Naplm00 Well-Known Member

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        I had the same exact thing happened to me when we picked up our car last year. Was a 100° day.

        I did the fuel line mod and added a carb spacer. I also added a reflective heat wrap on the new rubber line. in the long run I think I'm going to change it to something else because I really dislike the fuel line going over the valve cover.

        It was effective in eliminating vapor lock it's just unsightly and a pain in the ass when you want to remove the valve cover.

        Almost likely be doing another hard line from the fuel pump along the engine where the spark plugs are around the back of the motor and then to the carb.

        If you do add a spacer underneath the carb you'll most likely have to upjet as I did.

        My spacer came in a carburetor rebuild kit from Mike's carb parts didn't have to pay extra for it it was already there.
         
      • RustyRatRod

        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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        Have you verified it is vapor lock? True vapor lock is pretty rare......even with ethanol in the gas. The more ethanol, the easier it is to do it though, so if you have more than 10%, that might be what it is.
         
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        • Slantsix64

          Slantsix64 Well-Known Member

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          3 nipple fuel filter, and a thick carb gasket
           
        • RustyRatRod

          RustyRatRod Lemmie see your b00bs. FABO Gold Member

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          Nipple? Now I'm gettin vapor lock.
           
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          • Duggie

            Duggie Well-Known Member

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            That's my best guess. The fuel filler cap is a rattle fit, new fuel filter, and I drove real hard (extended high RPM) before the valve job trying to blow out 20 years of carbon from the previous owner driving it to the beach front each summer.

            I've had an ignition coil overheat and short out. It didn't act like that.

            In a previous life, I was lucky enough to ferry GA airplanes around the country for a local Cessna dealer. One I ferried from the factory was a Turbo 206 that needed a fuel boost pump before landing to prevent vapor lock. The engine would lope and die if the fuel boost was shut off before the plane was parked when the engine was hot.

            Driving the Dart back to the barn with the wet rag, "farm fix" it cruised without surging, but died at every down / up shift (letting off the gas). I've idled this engine a fair bit since purchase and it's never died until this hot day drive.

            Ethanol in WA state must be 10-15%.

            I'll keep that carb spacer in mind if the fuel line reroute doesn't completely cure the problem. I wondered too about the routing over the valve cover. The heater core hoses were short enough that I had to pull those to adjust the valves. Pain! After I finish rebuilding the heater box, I'll be looking at routing heater hoses like RustyRatRod did on his.

            Thanks you guys!
             
          • Duggie

            Duggie Well-Known Member

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            Did this mod over the weekend. Looks clean. Interestingly, my old fuel line routing over the exhaust manifold had the fuel filter positioned horizontally. I saw an old Mopar service video on YouTube that cautioned to not have the fuel filter horizontal because of vapor lock issues. They recommended vertical filter alignment, or at least an incline in the filter angle.
             
          • slantsixdan

            slantsixdan =..=

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            Lettuce know how it does for you.

            '61-'62 cars had that (no fuel filter as factory equipment in '60). They fixed it for '63…

            …as described here.
             
          • /sixchall

            /sixchall Well-Known Member

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            Since you’re talking about heat affecting fuel delivery and vapor locks. Living here in SoCal can during the hot summer mo. give us those triple digit days we’ve heard of. I tried to keep travel to and from car gatherings down to a soft roar, especially with black interiors and no A/C. I noticed the under hood temps can be really hot. My fuel line does route to the front of the engine across top of water pump with a clip. Adding Hooker headers the 3 into 1 asphalt dragger type. And a Super Six set-up. The steel tube headers create a lot of under hood heat so, fuel surging and intermittent vapor locks occurred. I picked up some 1/8” T6 aluminum cut out a spacer to go under carb with cut out for throttle travel and over toward valve cover. Mounted using 2 of the thick carb gaskets one above and one below spacer. Toward front of spacer I had a Pentastar ball milled into the metal and then had it polished which matches chrome valve cover. Did cut down amount of heat traveling upwards under carb.
             
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