Carb question
 

Do webers require supply pressure to operate or can they function(idle) until the bowl is empty?

As with any carb...the engine will run until the jet can no longer pick up fuel.
In most carbs...the jet sits up from the bottom of the bowl slightly...so there will be a little fuel left in the float chamber when the engine dies.
Bob

If there is any pressure in the float bowl, other than that created by the head of the fuel then the calibration of the jets will be lost.

The position of the jet and the associated head will influence how much the float bowls will empty at idle on combination with the vacuum pressure in the inlet manifold. These characteristics govern how much and to what level fuel wull be drawn.

The only reason fuel pumps of engines with carbs need to produce pressure is to overcome fuel line restictions to flow and should always the minimum possible.

Thanks!