MBK Nitro acceleration problem?

Hi guys!
I have Mbk Nitro full stock, it's top speed is 85km and it's fine for me, but it's acceleration is heavy(i tried a new Yamaha Vbelt and a 4,9 - 5 - 5,4 rollers), what should I do to get a better acceleration? Thnks!

 

Try 4.5g rollers

 

I was thinking about changing the rollers and the push spings, but I don't know what exactly fits my scooter!

 

Same as a jog. It's called a minerelli horizontal engine