Hi and welcome to Mightyram. Now this is something I personally haven't seen before - an alloy body variant of the second generation Mikuni carburettor. The emulsion tube should be a simple press in fit by hand but seeming your carb clearly has some internal corrosion issues I would recommend either replacing the whole carb with a good Mikuni or using a Weber which will be easier to rebuild, and will also improve economy and horsepower.