[MNVXer]

Reviving an old thread to give a conclusion that changing out the pump -did not- resolve the stumble. Nothing fixed it, including putting in a new 123 Distributor, until I went to a full Euro manifold system, replacing the SPICA manifold to Weber conversion set-up. My theory is that the rubber seals between the carbs and the SPICA manifold were old and started leaking air, changing the mixture, when the engine was at the 5300 -5500 rpm range.

Anyhow, conversion to the proper Alfa Weber set-up fixed the problem.

Thank you for wrapping this up. I saw that the thread was old, but it had a lot of good fuel-pump-carburetor-theory information. Its always nice to have an ending! That facet mount looked gigantic, I'm a bit surprised that it fit under there!