Very interesting Ian. I live in hope that a Mikuni would improve the starting of my Supa5 which is covered up and languishing in the shed as I had virtually given up on it but after reading your post, hope springs anew !
So could I ask the model/size of your Mikuni and who the supplier was.
PS I fitted the Vape system to it some years ago and found it to be great bit of kit.
Not one kickback since.