[Healeys] Vapor lock gas

WILLIAM B LAWRENCE ynotink at msn.com
Fri May 7 10:47:00 MDT 2021

During my jaunt to the west coast meet in Parksville, BC in 2012 I indulged in a tank of Premium non-ethanol fuel. As I recall it was priced by the liter and calculated to about $6.50 per gallon. The car loved it. The card, not so much...
From: Healeys <healeys-bounces at autox.team.net> on behalf of Bob Spidell <bspidell at comcast.net>
Sent: Friday, May 7, 2021 1:41 PM
To: Michael Salter <michaelsalter at gmail.com>
Cc: Healeys at autox.team.net <Healeys at autox.team.net>
Subject: Re: [Healeys] Vapor lock gas


On May 7, 2021, at 6:27 AM, Bob Spidell <bspidell at comcast.net> wrote:

In the ‘States, fuel is blended with ethanol (thanks to the corn lobby). Dunno about Canada.

On May 7, 2021, at 5:59 AM, Michael Salter <michaelsalter at gmail.com> wrote:

re: "Methanol[sic] lowers the boiling point ..."


Have I got that wrong Bob?

"Following the crude oil price shocks of the 1970’s, methanol blends for use in the onroad
vehicle fleet began extensive studies in the later 1970’s and the 1980’s. Based on
this early research, methanol blends containing up to 15 vol% (M15) were successfully
operated by automakers or oil companies in a number of large vehicle fleet trials (
~ 1000 vehicles each) in Sweden, Germany, New Zealand and China during that
time. Also during that time period, methanol gasoline blends containing as much as 5 vol% with co-solvent alcohols were
commercially introduced in Europe and the U.S.A. Because carburetted fuel systems with older elastomer parts were part of
vehicle fleets on the road at that time and had limited ability to handled high oxygen content in the fuel, the fully commercial
methanol blends were generally limited to 3 to 5 vol% of the gasoline blend with some co-solvents also added to provide fuel
stability. However, with today’s modern pressurised fuel injector systems using feedback control loops and also using more
advance fuel system materials, current experience suggests that methanol blends as high as 15 vol% (M15) of the gasoline
blend with adequate co-solvents and corrosion inhibitors can now be successfully used in today’s more modern vehicles in
use today. Many provinces in China have been commercially using M15 blends as early as 2005, and China’s M15 use has
been expanding because of very favourable economics compared to higher cost petroleum fuels."


On Thu, May 6, 2021 at 11:03 AM Bob Spidell <bspidell at comcast.net<mailto:bspidell at comcast.net>> wrote:
re: "Methanol[sic] lowers the boiling point ..."


On 5/6/2021 6:51 AM, Michael Salter wrote:
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.


On Mon., May 3, 2021, 2:58 p.m. Ken Fleming, <ahmg at aol.com<mailto: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.

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