[Healeys] Vapor lock gas

Alan Seigrist healey.nut at gmail.com
Thu May 6 08:02:25 MDT 2021

I have found that having the header and miniature heat shield to be ceramic
coated makes a huge difference in the engine bay but then transfers heat to
the exhaust, so it’s only good if you have an SS exhaust system and then
you need to insulate around the pump as Michael has said.  i just wrap
header tape around the exhaust pipe in that area and that is also effective,

On Thu, 6 May 2021 at 9:52 PM, Michael Salter <michaelsalter at gmail.com>

> Hi Ken, yes I think everyone with a 100 has encountered fuel delivery
> issues with modern fuels. Methanol lowers the boiling point of petrol to a
> point where it becomes a problem.
> With the 100 there are 2 distinct issues.
> Firstly, because the fuel pump and its associated lines are directly above
> the exhaust pipe, hot air heats them. The fuel in the suction side of the
> pump has, effectively, a lower boiling point than it would at atmospheric
> pressure. This fuel tends to boil if there isn't sufficient air circulation
> to keep the pump and lines cooled, as occurs while stopped in traffic on a
> hot day. True vapor lock occurs because the pump will not pump  sufficient
> volume of vapour to exceed the rate of its production by the boiling
> process.
> Secondly the carburetor float chambers and the small fuel passage to the
> jet are very close to the exhaust manifold.
> The manifold radiates lots of heat which heats them. Again when the car is
> moving at a reasonable pace the incoming air through the grille and around
> the radiator is sufficient to maintain the carburetor at a low enough
> temperature to prohibit boiling but, again when stopped in traffic this
> doesn't happen.
> I have managed to eliminate the first problem by installing a insulating
> sleeve from a modern car's AC hose over the fuel line from the tank to the
> pump.
> For the second I have made small heatshields from 24 gauge galvanized
> steel to shield as much as possible of the carburetors from the radiated
> heat. This has helped considerably but not completely eliminated the
> problem.
> For the most part neither of these modifications are visible and I have
> found that fuel delivery issues, although not completely eliminated, are
> manageable.
> I am considering installing a small blower and duct sourcing air from
> behind the grille to see how much difference that makes but if course that
> will be visible.
> Hope that helps, others may have found better solutions.
> M
> On Mon., May 3, 2021, 2:58 p.m. Ken Fleming, <ahmg at aol.com> wrote:
>> Michael , I thought you maybe have experience this ans have a solution .
>> On my Bn1 which is M spec with carbs, advance distributed, LeMans Cam and
>> Pistons has always suffered from what I call vapor lock of gas. Especially
>> in hot weather .
>> I am assuming the heat is from
>> Manifold and it placement near carbs or fuel pump/ battery near exhaust
>> play a role but I could be wrong . I have asked other owners and they seem
>> most of them not to have same problem. I do have a heat sheild added with
>> little result.
>> I am at a loss as to
>> What to do
>> Next , but have you experienced this and have any suggestions. Are my
>> assumptions
>> Correct on heat causing the issue.  Could today’s quality if gas be a
>> issue?
>> I recall reading this was a common issue for 100’s to have vapor issues.
>> Ken
>> Sent from my iPhone
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