Model B carb on stock Model A

[Synchro909]

The runners are different ,on the A manifold the ports neck down from where they mount to the ports, the RHD B one I have does not.
Lawrie

You are correct. I was talking about diameters. Clearly, in order to get that extra 10hp out of the B engine, carburettor and manifold were part of the "tweaks"