scratchndent to me it looks like the Loncin engine in your bike
much like the one used in this Apollo enduro (http://www.apollovehicle.com/Motorcy...W250T_328.html)
slightly different casings for the generator and clutch cover but i believe this also has the same engine
http://www.atomik.com.au/dirt-bike/e...-xr-250cc.html#

Kennon