I have tried the engine with the replacement carburettor. No good at all. I did manage to get it to fire and run for a 2 second burst. Tried a new plug, re-timed the engine using a newly machined converted spark plug as piston position stop similar to the one on Adrian Ciulei's video. Timing set to the recommended 30 deg.
I suspect weak spark, but Adrian assures me it is over 30 kv.
This problem is becoming intactable and I'm just about over it. I will give it one more week; if I don't fix it by then, it will be shelved and I will close this thread.