But those should run off the battery, for as long as that lasts anyhow.
The original question contained the phrase "when the battery is dead" (912 that is).
Anyhow, I have unsuccessfully tried to run my 914 without the pumps after a mishap where I unintentionally switched the pumps off. My fuel surface was perhaps 15 cm above the carburetors, but the turbo needs a fuel pressure of at least 0.25 bar above the boost pressure in the airbox.
/Bengt
/Bengt