You need a longer-term residence permit (for workers, spouses, etc.). You can't register a vehicle if you're here on a tourist visa. In fact, I don't think you can even get a Chinese driver's license without a residence permit (maybe someone can correct me on this one).

Also, to get the driver's license, you'll need to transfer your foreign license over and take a written test. You'll need a foreign license with a motorcycle endorsement if you want to go gas powered. Some regions will let you get a new license in China, but you'll have to take driver's ed and the technical test.

You'll also need a proper address to tie the registration to, and for gas powered scooters or other two wheel vehicles, it will have to be a house outside of the second ring road.

You may find it difficult, or impossible to get it properly registered in your circumstances. There are a few foreigners here that just go completely unlicensed, but you risk having your bike confiscated by the police, as well as the liability for any accidents as I mentioned above.

I am not sure about Kunming, but in many cities in China there are no new registrations for two stroke engined vehicles. Most 50cc mopeds are two strokes.
You do need a Chinese issued license. If you get caught on an unregistered motorbike you can get in a lot of trouble, it depends on how the cop is feeling and what the traffic police are clamping down on this month. A colleague of mine was stopped for riding an unregistered bike. He was not involved in any accident. He was jailed for 10 days (apparently it is within police powers to jail for 10 days without the need to go to court). He was then deported.
This actually happened.

@tigertiger: Was your colleague in Kunming? I'm not casting doubt on it, I just hadn't heard anything about it. It's certainly within the police's powers to do just that.

Yea, looks like there is a lot to consider. What about renting a small mopeds or scooters at Kun Ming? does that one sound more realistic in my case?

xiefei, this happens A LOT.

if its busy as hell and you play the ting bu dong card, they will let you go some times.

if they are bored,.and nothing is going on, they will confiscate the bike.

if you argue, and its obvious you speak chinese and know the rules they will detain and deport.

This happened in Shanghai, when they were having a crackdown on unregistered motos.