What country are you from ?
an RD50 can be hopped up all the normal 2 stroke ways
Mill the head for proper 'squish'.
Port the cylinder.
Put a tuned exhaust pipe on it.
Try here for parts http://www.50cc.nl/
Like this pipe they have for an RD50m
<IMG scr=" http://www.50cc.nl/plaatjes-onderd/1616.jpg"> ;
Be careful.. you need to get the RIGHT part for your model in your country.
These parts come from the Netherlands in Europe.
So you don't want the wrong part.
The cylinder porting and head milling can be done locally at any dirtbike shop near you.