This brings back memories of my old LHD Fiat 600 - named Lady Jane
I'm struggling to remember stuff but you have a choke lever by the gear lever? Also under the dash you have a "fast idle" rev lifter. Open ring pull cord.
Now as I recall the choke lever also opens the throttle plate a little.
Does the car start if you slightly depress the throttle pedal or pull the under dash fast idle control out?
What we are trying to establish here is if the carb throttle plate has gone out of synchronisation or that there is some other issue like partially blocked idle/start jets to blame.