An observation about the earlier suggestions to move the 276 float chamber forwards/backwards to counteract fuel surge.
When measured carefully, I found the mounting faces of my standard manifolds are not accurately vertical. This results in the bore of the rear carburettor sloping down a fair bit towards the engine, whereas the front carburettor bore slope slightly upward.
Consequently moving the float chamber alters the fuel height at the main jet quite appreciably, especially on the rear carburettor. Its also more pronounced if you have the long arm float chambers. I use the short arm ones and have fitted a sort of capstan to the mixture screws so they can be adjusted from the side when they are behind the float chambers.