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Thread: Vapour lock?

  1. #1
    Join Date
    Feb 2007
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    Essex, UK
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    Vapour lock?

    Had my first experience of (what I believe to be) vapour lock today.
    After a decent 20+ mile run the car started to run a little rough. I think I may have a little bit of dirt in one of the jets (well that’s what it was last time) as I pulled into my drive, it stumbled and died. Could I start the bugger? Nope. Waited a min or two and it started (same roughness)
    I guess if you’re going to get vapour lock, the hottest day of the year is the day to do it on!
    No room for phonelic (sp) spacer as the air filter nearly touches the bonnet. Any ideas?
    Ford 302 with Holley carb
    Simon
    WARNING: Translation of author's random thoughts may have resulted in the unintended introduction of grammatical errors, typos, technical inaccuracies, lies, propaganda, rhetoric, blasphemy, rambling, and/or exhibition of shocking levels of ignorance.

  2. #2
    Join Date
    Sep 2009
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    Leeds
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    2,863
    1/2" spacer and wrapped exhaust was my only fix for this
    Conny - A Carnival Red Metallic (paint code Ref: Jag CGG/1811) Southern Roadcraft V8 ( SRV8 ) with 383ci stroker chevy.

  3. #3
    Join Date
    Sep 2010
    Location
    Nova Scotia
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    808
    I had a similar problem and insulating the fuel line (as well as replacing it with steel vs. copper) pretty much eliminated the problem. You can see the details (with pic) here:

    http://www.cobraclub.com/forum/showt...t=60480&page=2

    Now I say "similar" which doesn't really mean all that much. My issue was more of trying to re-start after sitting for while. I never did know for sure if it was percolation or vapour-lock, and I'm not really sure I know the difference. From what I understand though, vapour-lock is when fuel in the lines vaporizes and the "air" bubble keeps fuel from flowing. Percolation is when the fuel in the float bowl boils away.

    Although my symptoms pointed towards the carbs boiling dry, insulating the fuel line from the pump to the carbs did the trick, so perhaps it was a bit of both. Like you, I had no room to add phenolic spacers, although a thin metal heat shield might work. It would extend out past the carb base and act as a cooling fin.

    A small diameter return line to the tank (so cool fuel is always flowing) would have been my next step after trying a heat shield, but fortunately I didn't need to do either.

    The other day it was well over 90degF out and I had no symptoms.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  4. #4
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    I think anything which extends out as a cooling fin on the carb (which can only work when there is a cool air draft over the surface) will also act as a thermal attractor, and potentially increase heat, coupled from the inlet manifold, at least when stationary.
    Crendon Chassis No.49
    Huddart FE428 + toploader

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  5. #5
    Join Date
    Sep 2010
    Location
    Nova Scotia
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    808
    Quote Originally Posted by KevinW View Post
    I think anything which extends out as a cooling fin on the carb (which can only work when there is a cool air draft over the surface) will also act as a thermal attractor, and potentially increase heat, coupled from the inlet manifold, at least when stationary.
    I think that might be kind of hard to know. Could be... maybe not. The air is cooler than the engine. The unknown is if the air just above the manifold is cooler. I think it is and most of that heat comes up through the base of the carb... but I admit. I don't really know.

    I have seen those metal heat shields advertised, although there's lots of things advertised that don't work...LOL.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  6. #6
    Join Date
    Feb 2007
    Location
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    Thanks gents, I’ll look into the spacer just in case I can squeeze a bit more room. I’ve also ordered some heat reflective sleeve for the fuel hose.
    I’ve also installed a manual fan switch in the car. Having driven my TR6 V8 for many years, I’m accustomed to flicking the fan on in queues “just in case”
    I was starting to panic in the cobra when the temp gauge started rising and it was a while before the thermostat kicked in. I’m sure being able to turn on the fans will assist with temps.
    Simon

  7. #7
    Join Date
    Apr 2004
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    East Leake, Nottinghamshire, England.
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    When I had the old RV8 in my car I used a heat spacer that consisted of 3 gaskets and 2 aluminum plates. Worked a treat and was only about 8mm thick all together from memory. Bought it from Reel Steel.

  8. #8
    Join Date
    Nov 2016
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    Stevenage
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    243
    Yup have 1/2 plastic type spacer.
    Carb has a reduced spacer ring between the carb and air filter to compensate and a 4 degree tilt forwards. Slight cut out on the dax bonnet on the inside edge and i can fit any filter inc the two inch long oval, not sure wheter they are any good though for air flow

  9. #9
    Join Date
    May 2016
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    Hockley ,Essex
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    56
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    Sort of Cobra related,

    Took Cob for a spin in the mid sun approx 38 deg ,no problems at all ,
    although I did have to rescue my wife in her Focus due to vapour lock !
    I did explain to her what to do but still had to go out and start it for her,
    you guessed it ,it stated after about ten seconds ,
    Chris.

  10. #10
    Join Date
    Feb 2007
    Location
    Essex, UK
    Posts
    3,882
    Well, no fun at all today!
    Nightmare journey to Carfest. Engine stopped 8 times in total. 10 mins with the bonnet up cooled things sufficiently to get it going again. Need to sort something soon.....☹️

    Simon

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