Question for jmarkaudio

[rgalajda]

Found this.

UNDER-STRUT PRIMARY
AIR BLEEDS
Under-strut primary air bleeds are used in some models
to give a smoother transfer from the low-speed circuit
to the high-speed circuit and increase part throttle
economy. This bleed is subject to venturi pressure
changes that follow engine load conditions. This is a
variable type bleed and under some conditions, could
act as a discharge port.

[GTO Geoff]

Thanks for that. That is the most logical explanation I have seen so far, makes sense.