Losing prime

[tsubaki]

The manual prime/choke may leak at times. For the most part it just scoots gas past the carbs and into the throat of the carbs, but usually leaks when rotated.
Being you bought the part to dismiss the VRO and have the fuel mix retrofit, let us know how it did.
On another note, you might have needed 2 fuel pumps at a cost of $80-$100 each. Also having to need to derive a vacuum siphon for the pumps and having to made a mounting bracket for them. The cost of the fuel mix pump ain't that bad considering the aggravation of the other installation.
aussie's electric pump idea will work but I've always been afraid of that installation.
While you are waiting, remove the stuff to and from the pump, reconnect to the carbs (if possible without a bunch of aggravation) to see if the floats are seating when the bubble is primed.