Just like most of the larger carbs, you need the proper flange.
I made one from some scrap metal for the carb side, and for now used the cutoff flange of a stock exhaust pipe for the intake side. Then a short length of rubber hose to connect them with a clamp with the two parts physically touching so its nice and sturdy. It works, but even after grinding the inside welds down on the exhaust flange the port is a bit small and shaped incorrectly so one day I'll make a proper one for that side too. Gotta keep it nice and short for clearance, which is better for top end power anyway.
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