Bill Freeman wrote:

Jeff's comment about sucking fuel is right on, you need
to have your pump inlet flooded with gravity feed from the
tanks.  My LE will gravity feed about 7 gph at the carb inlet
with both pumps off in level flight attitude.  So MAYBE  I
can do normal cruise with both pumps failed.  Hope to not test
this aspect, but it seems nice to have.

I have a friend with a "more stock" Long EZ fuel system
that has the electric boost pump located *above* the mech
pump and he had multiple occurrances of hot start vapor
locking of the pumps, since it was the highest point in the system
and would fill with vapor when hot soaked, esp with mogas, but
even with 100LL.  The engine would not start hot at all on warm days.
The solution for him was an *insulated* cooling
shroud and plenty of airflow when flying.  The pump stayed cool
in operation and the insulation keeps it cool (firewall mounted) during
ground heat soak after running.  Problem solved, but he avoids mogas.

I mounted my electric pump below the mech pump, so I can get fuel
pressure even if the mech pump is filled with vapor and thereby
disabled.

OOPS !!!   I was just thinking (hurt my head, too) and realized that
the electric pump is UPSTREAM of the mech pump, which is why
keeping it low and flooded can PUSH fuel thru the hot and (probably)
vapor-filled mech pump.  The reason that my friend's mech pump
couldn't clear the vapor is that the electric pump is upstream and is
full of vapor and is hot.  Essentially infinite vapor supply until
it cools down.  In case anyone ever wondered why a positive displacement
pump can't pump with vapor at the inlet - it can, but it pumps a slug of
vapor which condenses as the pressure increases at the pump outlet,
and the vapor represents only a tiny drop when reliquified.  So the pump
still pumps, just with a 100X or more flow rate reduction, which is bad.

I have flown my system with mogas at a ramp temp of 106 F after a
two hour heat soak (from flying in) and no fuel pressure fluctuations
or problems.  Was concerned the 1st time, but it works fine and I use
mogas most of the time (Amoco Blue).

Bill

 
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