Re: Vapour lock

[Glenn Merrell <gmerrel@domain.elided>]

Hello All,
    We here in the Western USA at altitude know vapor lock very well.
It is usually experienced only on carburetor vehicles, and is caused by
the heat of the engine vaporizing the fuel in either the fuel line,
carburetor fuel bowl, or in the intake manifold.  The symptom is that
the engine seems starved for fuel, or flooded.  On cars with accelerator
pumps, pumping the pedal will net no fuel being squirted into the
intake.
    What is happening in most occurrences is that the vaporized fuel in
the fuel bowl will pressurize the bowl closing the fuel float if the
bowl is not properly vented, starving the engine of fuel.  In the case
of metal fuel lines, a pressure bubble builds in the fuel line usually
at the fuel filter, keeping the fuel from flowing.  In the last case of
vapor lock in the intake manifold, the intake may appear to be flooded
with fuel, and sometimes can cause an engine fire.
    I'm sure that some other responses can make this more complicated,
but that is it in a nutshell.
To correct vapor lock symptoms, an insulating spacer gasket may be added
to the intake manifold to isolate the carbs from the manifold,
reinforced polypropylene fuel line to replace metal fuel lines around
the engine, or rerouting the fuel line, and removing some of the heat
from the engine compartment always helps.  Fuel additives may help, but
only marginally.

Regards,
Glenn Merrell
"Keep Your Stag Cool, Install a NEW Composite Cowl Today"
http://pw1.netcom.com/~gmerrel/stagcowl001.html