David Mount

I am looking for any information regarding this brass carburettor, which is fitted to a circa 1929 1750 Alfa Romeo Gran Turisimo. The car is running very rich, with sooty smoke from the exhaust. Efforts at tuning seems to make no appreciable difference, air intake being small & probably not helped by ethanol fuel. albeit using 95 super grade. The carburettor is apparently an original fitting, manufactured under licence, as the detachable top contains the words 'Brevetatto Zenith'., so presumably manufactured under licence. Have tried weaker main jets, but don't want to risk damage to engine which runs on rich side anyway. The petrol intake is controlled by a butterfly valve system, which rises to open the petrol intake, closing. when chamber is full. petrol flow pressure is controlled by an adjustable pressure valve, which again appears to make no difference. Think problem is in part at least ethanol related, but question remains as to, short of seeking out a suitable alternative carburettor type, whether anything can be done to deal with this problem & thus avoid risk of engine damage. Any ideas & has anyone come across this carburettor type, which seemingly is not wholly dissimilar to ones fitted to other car types.