Best exhaust (expansion chamber) for 50cc Honda Dio AF34

[Ryan]

Hi
After my old exhaust (expansion chamber) fell apart and I could no longer reweild it, I bought a cheap expansion chamber off the internet. The top speed has now dropped from around 70 - 75 kph to a stock standard 60 kph. I have changed the jets and done a plug chop but have no improvement in speed. I obviously need to replace the exhaust with something decent. Can anyone please recommend a good expansion chamber for a 50cc Honda Dio AF34e? I am also currently running in a new belt, any advice on how to go about this would also be appreciated. Thank you.