So there is no spark when it dies?
What about vent hole in gas cap?
Do you have an outside coil?
If yes, check all connections, use some electrical cleaner to clean this thing. The reason I mention coil I've had Columbia with Solo engine and it was doing this same thing, replaced condenser- still this same problem, finally I noticed that coil is all greasy so I replaced it with another one and that fixed the problem. Peugeot 103SP is using standard Bosh coil I believe so maybe give it the try.
I have 103 and also Batavus Grand Prix with Peugeot engine.
Those are good engines.
Niech zyje bigos