Carburettors do wear eventually, replacing internal parts like the float, jets and adjustment screws/springs with new components usually gets everything back into shape.
But, also check that the fuel being used is not contaminated, with water or particulates and is fresh - fuel has a relatively short shelf life and will soon go off - the smell will inform as well as anything else.
An alternative, short and easy way to refurb the carbs is to simply fit complete new carburettor assemblies - more costly but saves a lot of time. Time also has value?
Other carburettor related parts you may wish to consider:
Make full use of our online schematic to ensure you order the correct parts and correct quantities.
Add as many parts as you wish to the same shopping cart, new gaskets, seals, shiny new screws 985800401498580040089780304010 & nuts 9538003600 for example, and stil only pay the same single fixed price shipping cost.
Be aware that this component may have other applications within the Yamaha model range.