[freebeard]

Well there goes suggesting you get something other than the most basic carburettor ever to be fitted with a choke. You *could* modify one to have an annular discharge venturi, or a booster, or a central discharge point (all of which will improve atomisation) but that's all more difficult to do than finding another manifold and modifying it to fit a progressive dual-throat carb.

https://en.wikipedia.org/wiki/Reece_Fish_Carburettor

Volkswagen downdraught set

The pictures below show a pair of Reece Fish carburettors with manifold tubing suitable for an air-cooled Volkswagen engine. Note that Reece Fish manufactured the tubing and manifolds as part of an after-market kit for this vehicle.