1 - fuel avg - its not always about the carburetor, before messing with the carby - igniton system needs to be checked and corrected if needed
ignition system includes:
distributor, ignitor gaps, vacuum and mechanical advance check
ignition coil for any current leakage, coil health
ignition wires - coil to distributor to spark plugs
spark plugs - correct heat range, wear and tear etc
noise suppressor / condenser.
once all of the above is checked / verified / corrected. only then you can proceed to work on the carburetor.
Now coming to the carby, you also need to make sure you have the correct primary and secondary jets for your engine. mechanics here love to install smaller jets which results in a lean running engine ruining its performance, economy and reliability.
the butterfly / throttle blades cannot just be made by any machinist - they need an experienced / well versed machinist to make them right.
why was the cylinder head removed?
