Hi!
That's the kind of knowledge you put in the file of "Unimportance things" . Just like "How many amps does a glow plug draw"?

The answer is that that silencer pressure is not enough...! The weight of the fuel inside the tank cannot be compensated for by just using silencer pressure. That's why we must set our engines a little rich at the beginning of the flight to compensate for the loss of fuel pressure when the tank empties.