[TR] Vapor lock?

Randall tr3driver at ca.rr.com
Sun Sep 7 15:00:11 MDT 2008


> A few weeks ago there was a thread on vapor lock.  I am 
> unclear as to where this will occur.  Does it happen only in 
> the fuel pump or can it occur in the lines too?

Kind of depends on your definitions, Tom.  As I learned it, "vapor lock" is
a fuel pump problem, basically that the pump won't move fuel when it's full
of fuel vapor instead of liquid fuel.  Of course, if the fuel boils (turns
into vapor) in the line ahead of the pump, then the vapor will eventually be
sucked into the pump to potentially cause vapor lock.

But, lots of folks describe any kind of fuel boiling/vapor problem as "vapor
lock", including fuel boiling in the float bowls, jets or even in the lines
after the fuel pump.  The major distinction, as I see it, is that all these
problems cause the mixture to go way rich (too much fuel in the cylinders);
while "real" vapor lock causes lean mixture (no fuel to the cylinders).

I'll add that in 40 years of futzing around with old cars, I have never seen
anything I believe to be vapor lock.  All of my problems with fuel pumps
that don't pump have turned out to be other issues, like crud in the valve
or line, stuck float valves, etc.

Fuel boiling in the bowls and jets (percolation) has been much more common
in my experience.

Randall


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