No power on pronto 50cc

[ozjeff]

Hi everyone I am a newby from Oz and recently bought my son a 50cc Bug pronto (Yup50?)
It starts first time and idles smoothly but at full throttle won't get more than 20kph and can't even make it up the smallest hill.
So far I have:
-replaced drive belt
-checked rollers (but didn't check diameter just for flat spots)
-New fuel filter
- checked air cleaner
- cleaned carby
- New spark plug
Still no luck! Any ideas where I should go from here?
My thoughts are to do a compression test next and also check the rollers for diameter.
Your suggestions welcome.

[ozjeff]

Finally discovered it is a clogged exhaust.
I am going to try to cook my exhaust to get the rubbish out so will see how we go.
However also trying to see what is available for an aftermarket exhaust/muffler
Can anyone tell me what motor the 2009 Kymco Yup 50 two stroke motor is based on?
My model is actually called a Kymco Bug pronto in Australia but as far as I can see it's a Yup 50 in Asia. No idea what its called in the US?
Anyway if I know what the motor is cloned from I will know what I am looking for muffler wise. Also what its called in the US would be useful.
Thanks.