[Gaz64]

The reason it is popular with the 911 owners is the Weber IDA-3C has the main and idle jets on the side of the float bowl not in the bottom centre of the bowl like an IDA, IDF or DCOE.

The fuel could run away and expose the main jets in a 3C, but that condition is unlikely to happen with an IDA, IDF or DCOE.

The jets in the performance 2 barrels are centred in the float bowl for the reason of constant fuel level in the main well regardless of cornering forces.
Also the reason for the shape of the float.