Because it's misfiring on one cylinder, then turning back on - like kid playing with light switch.
First let me say that I am no guru when it comes to carbed engines.
But when you say that its misfiring on one cylinder - of course it is - its a wasted spark system and only one cylinder fires at any time from the same, dual output coil. The problem is, how can you tell, from the video clips, whether its the same cylinder every time?
If Ignition pick-up or ignition computer it would be both cylinders cutting out or randomly switching from side to side
Personally I tend to think that the misfire is randomly switching from side to side, since the pickup, ignition coil and igniter unit are all common to both cylinders.
The ignition coil may test OK cold, but when it gets hot, problems show up.
I agree, the main suspect would be the coil or its HT cables. The igniter units are far less forgiving and would tend to cut the engine completely as load on it increased. As for the pickup coil, I guess that an incorrect air gap could cause these symptoms but apart from that, experiences on here show that the pickup coil goes open circuit and cuts both cylinders until it cools down again.