Last year I bought a 125cc bike Modenas brand, most likely unknown to you. It is a moped. http://www.modenas.com.my/v2motorcycle.asp?id=70
It can go as fast as 110 km/h enough for the city and not only.
However I gave it to a family person for a while and nearly destroyed it! Luckily the frame is ok and the bike goes straight..
He destroyed the exhaust valve, and 1.5 L oil consumption per 2000km! 1L capacity
When I noticed it after 200 km running on low oil about 600 ml were missing, believing that it was serviced and ok. He had removed the air filter, and put a noisy exhaust.
I don't want to say much but I fixed everything I had the tools to do. Professional technicians told me that there is a problem with the piston/ring/cylinder.. and that it needs to be fixed... So I did... Cylinder got larger by 0.5mm ...
Here are some photos of the old piston... Do you see any problem with this piston?
Because i find that is has little problem an cant explain how this condition can cause so serous oil consumption problem?
Until now, after the service it seems to be running well... Oil level seems stable for the first 200 km.