Old carburetors and their associated linkages get very grotty with age, general dirt accumulation and fuel leaks/weeps. They can end up covered in black gunk and looking like they have been barbecued. Degreasers and most similar products won’t shift the black gunk which is a residue composed of fuel dye and evaporated hydrocarbons.

The answer is quite simple. Use lacquer thinners or acetone to remove this grunge. Use an old retired [shaggy dog] tooth brush or a similar stiff brush and scrub the carby whilst keeping the brush wet with the thinners or acetone. If the carbys are still mounted on the engine spread a good thick layer of news paper under the work area to catch the drips etc. as you don’t want to splatter the painted areas inside the engine bay with these solvents.[they will eat the paint]

You will be genuinely surprised at how easy it is to clean your carbys using this method. Note that in the end the toothbrush will eventually fail, as the solvents will destroy the plastic handle so don’t use the one with which you are currently brushing your teeth.

Please take the usual precautions when using highly flammable solvents. Use a well ventilated area with no smoking or fire sources in the vicinity and personal protection for your eyes, lungs, skin etc.