Hi, thank you very much to everyone you responded to my request.
I was given the mikuni carb by an engineer who made two sleeves on a lathe to suit the inlet manifold and the airbox rubber hose.
I spoke to Allens Carbs who said that mikuni have two branches to their business. “Original equipmnet” and “after market” and often the after market jets are incompatible with original equipment carbs which is what i think i have.
I not going purchase jets etc to find that they are unsuitable for my carb so have put the modification on hold for the moment. regards, John