Vivacity 50cc 2t jetting

Hi

I bought a vivacity about 2 months back, it came with a leo vince, but ran poorly, due to it having a mix of 8, 9g rollers , its now got 5.5 in after trying 8 and 6.5 ..i like it now ..but i heard i should upjet, it looks like its either 50 or 54 in the moment, writing is small so what would be ideal or a good starting point ..i have some from 50-72

 

Start with biggest jet, run it until the plug colour is a nice dark chocolate brown colour.