Modern petrol, particularly low-end cheaper super-market supplied fuel, can play havoc with carburettor internals.
This is particularly evident when the machine has been standing for long periods, a common occurrence with motorcycles frequently laid up for the cold winter months.
The old, stale fuel tends to "varnish" the internals, and the bioethanol element of the fuel even causing corrosion to the working areas of the carb.
Sonic cleaning of the internals can help, but where it can't this and perhaps some of the components listed below maybe required:
Add as many components as you wish to the same shopping cart, new fuel line clips 920371142 & O-ring seals 920551053 for example, and still only pay the same single fixed price shipping cost.