Comment from Gary Casey:  What if the shaft seal leaked air into the
pump, even though it is effective in keeping the fuel from leaking out.
After a few minutes at altitude it has enough air in it to essentially
vapor lock for a few seconds.  Wouldn't it be good to put the pump in an
insulated compartment forward of the firewall?  I know, no room.

Gary,
This is a scenario we considered.  As the pump is running continuously
above 10k, nothing really changes if the 5psi differential were pushing
air in through a leak.  I would also expect to find blue stain
somewhere, which there was none.  We also plugged the drain/vent which
would or could be the potential source.  This did not help.

Again for those who did not catch the previous posts, the only thing
that has solved the hesitation on switching tanks the first time has
been to lower the fuel pump to the floor.  I climb full rich to
altitude, pull back the RPM and Manifold to cruise, switch tanks and
then lean.  No more hesitations in 17 flight to FL 220-250.

Mark at Lancair has pictures.  markm@lancair.com

Carl Cadwell, N25CL, IVP