Thanks Todd, Rusty, and Al for the responses to my fuel system concerns.

Todd’s observation that the capacitive fuel gauge indications are reliable
when the tanks are near empty is what I needed to hear.

I took Rusty’s suggestion and investigated the source of the bubbles in the
fuel lines further.  When the high pressure fuel pump in the plane is
running, there are no bubbles between the tank and the pump, no bubbles in
the fuel rail or lines between the pump and the pressure regulator, and
there are bubbles in the return line between the pressure regulator and the
wing tank.  As a separate test, I connected a fuel pressure regulator to the
RX7 donor car’s fuel tank which was filled with fuel and had the original
submerged fuel pump in it with a clean inlet sock.  Running the pump in this
setup gave the same results:  bubbles in the return line, but nowhere else.

Al’s suggestion is probably correct that the bubbles are air which was
originally dissolved in the fuel rather than fuel vapor as I had originally
thought.  Fuel vapor should rapidly recondense, but redissolving the air
into the fuel would probably be a slower process, thus the bubbles persist.
Using the submerged fuel pump as he recommended did not change what was
observed, but still is a good idea for the reasons he stated.  

I don’t think there is a problem when the fuel is returned to the large wing
tank where it would be unlikely for the bubbles to get into the line
supplying the pump.  It could be an issue, however, if the fuel is returned
to a smaller header tank depending on how the header tank is constructed and
vented.

If the fuel is recirculated long enough, and if the bubbles are really air;
the dissolved air should be eventually nearly eliminated from the system,
but I didn't run the pump long enough to see if this is true.  I haven’t
tried the tests with avgas, either.

My apologies to the list if this is common knowledge.  


Steve Boese, WY, RV6A, 13B NA, EC2, RD1A