So 2 options.
Blue pill - Replace all offending brassware.
Red pill - Replace the lot with the later BDS28 carbs which feature better chokes, parts that are far cheaper & easier to source. These do incorporate a throttle position sensor & electric carb heaters, so further modding would be required. The biggest problem being the majority that come up for sale look like they went down with the Titanic.
So blue pill it is. After some extensive research a Keyster carb kit (part No.KY-0628NRR) was sourced via fleabay for slightly less than a kings ransom but somewhat cheaper than buying the parts separately. Changeover went smoothly, float levels were reset dry & double checked wet. 2 diaphragms had slight splits but were replaced with parts from a freebie donor set of carbs. Carbs refitted with the assistance of ancient Anglo Saxon profanities. Fired up, a bit of black smoke at high revs initially probably from the sooty 2&4 cylinders, but this quickly cleared. Carbs balanced & running smooth.
Test Ride - WOW what a difference, smooth as silk throughout the rev range, all hesitancy gone.
A thousand Huzza's...........but what would have happened had I taken the red pill?
....don't even think about it.