Garelli can be fast.
They make 70cc kits for them.
The 13.13 is wayy to small if you will be running a kit. The stock carb is already 14.12 SHA which you can just drill bigger. Anything 16mm+ will do for kits.
Along with a kit, bigger carb, nice modded expansion pipe and regearing. Garellis can easily hit mid 40's - 50. Although to get to these speeds you will definitely need good port work.
There has been numerous threads on this subject. Search will provide a good list of information.