Uno Slipping timing belt

[s130]

I'm only foggily remembering this, but back many years ago I've come across carbs with shut off valves whose main function was to cut fuel to the jets as soon as the ignition was killed. I think this came along when manufacturers started experimenting with weaker fuel mixtures for better economy and less emissions but because designs were more basic than today engines were prone to running on with self detonating combustion taking place - not requiring a spark. Some engines would splutter and even run backwards for a few revs, I can hear it in my mind!

Probably so but I never saw this on a Fiat engine.

What would have prompted this jet shut off on ignition off is the move from low compression engines 8:1 to high compression engines 10:1+ coupled with leaner mixtures. All efficiency, emissions and performance based enhancements.