Top speed problem

I have a SYM yet Basix 2007 2 stroke and speed blocks at 65kmh. Parts I have on new 50cc cylinder, new unblocked exhaust Tecnigas Q-tre, Mallossi clutch, 6.5gram rollers and a 17.5mm carb. I used to have a 70cc cylinder but it ran the same. Any ideas why id does that?

 

I dont think so because when I hit 50kmh my engine goes to like 12000 rpm ( it seems like I have a powerband at 50kmh ) and goes to 65kmh still screaming.
https://www.youtube.com/shorts/6z_I7E46MxY

 

Use heavier rollers, has it got the correct drive belt?

 

I have the same top speed with 3,4g rollers and 6,5g rollers. Yes it does have the right drive belt.