In over carburetored situations such as this a typical slide carb (be it flat or round) will bog the engine when floored because the instant the throttle slide is lifts the carb goes to the needle jet/jet needle circuit and the main circuit. However, as this happens the instant it does the air flow is the same as you had when you smashed the throttle - so at idle you will have a little bit of airflow then when floored you get tons on fuel in and this floods it.

Now this is why CV carbs are good (flat side CV would be awesome!) because the throttle slides lift exactly at the rate the engine needs it (even when floored).

My Mikuni BS34's flow as much as 42 and possibly 45mm Webber DCOE as the venturi in a Webber is steeped down. (42's generally have 34mm venturies and so do 45's depending on the jetting). But after jetting my BS34's correctly you get the flow of a decent Webber and If I want I can set the idle to like 300rpm (you can watch the fan tick over lol). Plus even at 300rpm when you floor it the engine spools instantly with no bog or hesitation.

The only problem I'm having is that my idle is slightly rich. Im using a 42.5 pilot and 160 air (stock Datsun A12 is 43 pilot and 220 air), but after drilling my air jet to 220 its worse (even more rich - go figure). Removing the air jet defies logic as the fuel air is so rich the car hardly idles.

Fun and games - tell you what though, as much as I love a carbie for its mechanical simplicity and durability, changing the injector pulse duration and using a wide band O2 to tune seems a hell of a lot easier; I reckon I'll give EFI a go in the future.