Piaggio bogs / doesnt speed up

I have a stock piaggio zip 50cc ( 2001 ) with a sprots exhaust.

Nothing has been modified to the carb / variator.
So the issue is when i ride at full speed, at 80/85% throttle the bike gains speed normaly and reaches tops speed which is about 52mph. But when i use the full ammount of throttle 100% the engine sound tone goes down and doesnt pickup as fast at 85%

Can someone help me with the issue. Idle is fine ect. 53 main jet on the stock 17.5mm carb.

 

Main jet is either too big or small. Sounds like too big actually.

 

Seriously? Too big? Its only 53 main jet and like thats stock. Iv removed the restrictions (brass plate and washer)

 

Yeah it's weird but it does sound like it's too big.
It's a bit like that sometimes though

 

Mine litteraly was my 2 air flows that went to the bike .. the carb and the one that goes to the top of the cylinder put the air filter on correctly and now my bike goes to full speed