Check to see if your auto parts store carries a gallon can of GUNK carberatur cleaner or some other brand. I see you are in the UK so I don't know if they are as strict about VOC's as we are here. The old stuff worked muck better then this new environment friendly version. Completely disassemble your carb and soak in the solvent for an hour or two then blow through all ports with compressed air or the aerosol can of carb cleaner.
