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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@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. Especiall=
y
> 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 see=
m
> 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=E2=80=99s quality if gas =
be a
> issue?
> I recall reading this was a common issue for 100=E2=80=99s to have vapor =
issues.
> Ken
>
> Sent from my iPhone
>
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<div dir=3D"auto">Hi Ken, yes I think everyone with a 100 has encountered f=
uel delivery issues with modern fuels. Methanol lowers the boiling point of=
petrol to a point where it becomes a problem.=C2=A0<div dir=3D"auto">With =
the 100 there are 2 distinct issues.=C2=A0</div><div dir=3D"auto"><br></div=
><div dir=3D"auto">Firstly, because the fuel pump and its associated lines =
are directly above the exhaust pipe, hot air heats them. The fuel in the su=
ction side of the pump has, effectively, a lower boiling point than it woul=
d at atmospheric pressure. This fuel tends to boil if there isn't suffi=
cient air circulation to keep the pump and lines cooled, as occurs while st=
opped in traffic on a hot day. True vapor lock occurs because the pump will=
not pump=C2=A0 sufficient volume of vapour to exceed the rate of its produ=
ction by the boiling process.</div><div dir=3D"auto"><br></div><div dir=3D"=
auto">Secondly the carburetor float chambers and the small fuel passage to =
the jet are very close to the exhaust manifold.=C2=A0</div><div dir=3D"auto=
">The manifold radiates lots of heat which heats them. Again when the car i=
s moving at a reasonable pace the incoming air through the grille and aroun=
d the radiator is sufficient to maintain the carburetor at a low enough tem=
perature to prohibit boiling but, again when stopped in traffic this doesn&=
#39;t happen.</div><div dir=3D"auto"><br></div><div dir=3D"auto">I have man=
aged 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.</d=
iv><div dir=3D"auto"><br></div><div dir=3D"auto">For the second I have made=
small heatshields from 24 gauge galvanized steel to shield as much as poss=
ible of the carburetors from the radiated heat. This has helped considerabl=
y but not completely eliminated the problem.=C2=A0</div><div dir=3D"auto"><=
br></div><div dir=3D"auto">For the most part neither of these modifications=
are visible and I have found that fuel delivery issues, although not compl=
etely eliminated, are manageable.=C2=A0</div><div dir=3D"auto">I am conside=
ring 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.<=
/div><div dir=3D"auto">Hope that helps, others may have found better soluti=
ons.=C2=A0</div><div dir=3D"auto"><br></div><div dir=3D"auto">M</div><div d=
ir=3D"auto"><br></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr"=
class=3D"gmail_attr">On Mon., May 3, 2021, 2:58 p.m. Ken Fleming, <<a h=
ref=3D"mailto:ahmg@aol.com";>ahmg@aol.com</a>> wrote:<br></div><blockquot=
e class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc sol=
id;padding-left:1ex">Michael , I thought you maybe have experience this ans=
have a solution . On my Bn1 which is M spec with carbs, advance distribute=
d, LeMans Cam and Pistons has always suffered from what I call vapor lock o=
f gas. Especially in hot weather . <br>
I am assuming the heat is from<br>
Manifold and it placement near carbs or fuel pump/ battery near exhaust pla=
y a role but I could be wrong . I have asked other owners and they seem mos=
t of them not to have same problem. I do have a heat sheild added with litt=
le result.<br>
I am at a loss as to<br>
What to do<br>
Next , but have you experienced this and have any suggestions. Are my assum=
ptions<br>
Correct on heat causing the issue.=C2=A0 Could today=E2=80=99s quality if g=
as be a issue?<br>
I recall reading this was a common issue for 100=E2=80=99s to have vapor is=
sues. <br>
Ken<br>
<br>
Sent from my iPhone<br>
</blockquote></div>
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