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DGV carb fuel boiling after shutoff

Discussion in '"Stock" Alpine' started by mightyohm, Aug 12, 2019.

  1. mightyohm

    mightyohm Gold Level Sponsor

    Has anyone else seen this? After shutting the car off, I can hear the fuel boiling in the carb, and if I take off the air filter housing I can see some of it percolating into the intake.

    It's well documented on the Opel GT and BMW 2002 forums but I haven't seen anyone on the Sunbeam forums talking about it. Apparently the ethanol in the gas makes the problem worse. It's pretty much impossible to find ethanol-free gas up here.

    I think our car has had this issue for a long time but I never paid much attention to it. It may be worse on the new motor, which has an intake without a water passage (though I suspect folks will disagree, and it's not clear to me in the hot water would primarily heat the intake or primarily cool it from the hot headers below).

    Some of the boiling fuel winds up in the intake, which seems like a "bad thing" for the rings.
     
  2. Barry

    Barry Platinum Level Sponsor

    Depending on the blend / additives / altitude, some components of gasoline can start to boil as low as 100 degrees F., so "percolating" in the carburetor is not a surprise. At sea level, ethanol boils at 173 degrees F., so .....

    The carburetor(s) on a Series Alpine engine is directly above the exhaust manifold, so fresh / cool air flow and radiant heat shields are probably a good idea.
     
    Last edited: Aug 13, 2019
  3. Ashfried

    Ashfried Gold Level Sponsor

    I use to have a gas boiling problem. I did a couple things:
    1. put in an electronic fuel pump
    2. Changed the plastic fuel line from fuel pump to carbs with a stanless steel line that stays much further away from the manafold. See pic below.
    I'm not sure which fixed it, but it has not happened again and it has been a couple years. upload_2019-8-12_13-29-8.png
     
  4. alpine_64

    alpine_64 Donation Time

    John

    If you are running the DGV the factory had a pholenic spacer ( insulator) between the carb amd manifold to prevent heat soak. If the fuel is vaporizing in the carb bowls that will be the issue.

    If in the fuel line, check its routing near exausts or other hot spots and insulate.
     
  5. mightyohm

    mightyohm Gold Level Sponsor

    Barry,

    I'm going to try fabricating a heat shield out of stainless or aluminum and see what that does.

    Ash - the pic is helpful. Looks like your line crosses in front of the engine block. How was the stainless line to work with? Easy to bend? Is there a good source for stainless line & fittings?

    Michael -

    I've got the carb spacer/insulator but it looks to be made of plastic, not phenolic. I ordered a phenolic one which should be a better insulator. (I may stack two of them together if I can fit them.)

    I ordered some insulation for the fuel line and I'm going to try to change the fuel line routing. Right now I have a rubber hose that wraps around the back of the valve cover and crosses over the intake manifold. Probably not the best setup.
     
  6. Ashfried

    Ashfried Gold Level Sponsor

    I do not remember where I got the Stainless line, but I used a small pipe bender and it was easy. I did not uses fittings. I went from hose to steel pipe and from pipe to hose at the carb T. Have you worked out where the gas is boiling? For me it was in the mechanical fuel pump. I could see it boiling in the glass jar. That is why I went to an electric pump installed nowhere near anything hot.
     
  7. mightyohm

    mightyohm Gold Level Sponsor

    I've seen the gas in the pump boil on a really hot day (and had to wait a few minutes for things to cool down), but the current issue is that the gas is boiling in the carb itself. On the DGV you can look down into the float bowl with the aircleaner off and see the fuel boiling. You can hear it with the hood up. Vapor lock is bad but fuel boiling in the carb is worse since it winds up spilling into the intake and washing down the cylinders.
     
  8. 65beam

    65beam Platinum Level Sponsor

    Michael said it best. If you have an original series 3 or 4 intake there was a spacer between the carb and intake . This was used to isolate the carb from the heat of the manifold. Keep in mind that the intake and exhaust manifolds are bolted together to the head so the heat from the exhaust will pass to the intake manifold. The use of this spacer with an original intake also eliminates mods to the intake to allow the use of a 32/36 Weber. I don't have access to my photos at this time so I can't show you the spacer.
     
  9. Tim R

    Tim R Silver Level Sponsor

    We have had this issue with cars in the UK and it gets worse when we tour on the continent (higher ethanol content).

    In addition to the ideas suggested here we have wrapped the rubber pipes with heat reflective material to lower the temperature and on some cars we have fitted electric pumps and then routed the fuel pipe all around the back of the engine bay and to the carb. This keeps it well away from everything hot and ends the problem completely.
     

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