hello..i need some advise from pro here..anyone who used to scooter especially..

i have a problem with my scooter. after reaching 60km/h..my motor suddenly became 'semput'...cannot reach higher than 60km/h..

i've try many solution including setting the timing, change the CDI and service carburator..the result turn the same after a few days..

anybody can help me solve this problem?? i had really hard days travelling slow with my scooter..

my spec..

Suzuki VS150(just bought last year.. )
i used the custom exhaust, double small pipe...
CDI change to CDI VS 125...