Piaggio zip SP spitting loads of black oil

Hi so I recently bought i Piaggio zip sp 2 stroke and i recently put a Tecnigas next r exhaust on and since then it’s been spitting black oil out the exhaust I think it’s 2 stroke and petrol that’s not being fully burnt I have a 60 main jet in the carb I’m really new to all this and this is my first bike so any help would be appreciated.

 

Check spark plug colour to see if it's rich ?

 

Spark plug looked clean maybe slighly black but more wet looking than oily

 

It need's to be a chocolate brown colour, if it's black it's too rich.