nsr250agr wrote:
2.Where is located the engine number??Cause i may buy a nsr engine and i want to know if it's a mc18 or a mc21...

The number on all normal road bike NSR engines starts MC16 so is no help whatso ever.

I'm not sure if you can tell the mc18 from the mc21 cases without taking them apart and as '21 barrels bolt onto '18 cases that's no guarantee either.
Steve or Andy may know better.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread