I suffered that problem with a Weber DCD 28/36 back in 1977. Over 100mph on the speedo of my modded Escort when the cabin filled with petrol fumes. Ignition off, as instantly as possible, and coasted to a halt the end of the short Tring motorway. Lucky that the ignition system was sound and at the front of the engine. Fuel was still boiling off the cylinder head when I carefully released the bonnet. A very lucky escape.