You have posted this in the Plus 4/ Plus 6 CX arena, so it may not be seen by classic +8 owners!
Before chasing fuelling issues, I would carry a spare spark plug when next going out and if the engine fails again, take off a plug lead and attach it to the spare plug. Crank the engine and with the body of the plug resting on earthed metal, see if there is a visible spark.
I have known of faulty rotor arms in the distributor causing intermittent failures. Cheap and easy to replace so worth a try?
