I went up to Electrex World which is just up the road at Stoke Row, to pick up a pick-up.
They sell a replacement for Ducati kokasan for £36.
https://www.electrexworld.co.uk/cgi-...2ehtml#SID=403
I had a long chat with one of the techs about the issues I was having and his view was that it was highly unlikely to be the pick up coil.
"They either work or they dont"
On the subject of coil impedance, he said it wasnt the coil impedance that was critical, but its inductance, and inductance can be achieved by various combinations of winding thickness and turns, hence why coils of different resistance may still work.
OEM resistance is 100 ohms, whereas these replacements are 460 ohms.
The upshot of the conversation is that only leaves the vertical carb as the culprit having swopped everything else (and it being unlikely to be the pick up.)
So the carbs will be coming off again tomorrow for another really good look in the LH one.
And hopefully another trip to Electrex World to return the pick up unopened.