MZ/MuZ Riders

Hello, I'm new here. Spend most of the year in Canada but generally manage to get over to the Isle of Skye in summer to ride my 1984 MZ TS 125 "Alpine." Bought it new, but someone told me it is now a Classic! Last summer the bike crept about and passed its MOT etc. but when I first started it up after two years' storage - it started on second kick! - the engine raced out of control and I think something was damaged, because the engine noise is not pleasant. I suspect my easiest route is to try and replace the engine, but I have had no joy at all finding one. Any suggestions please? Very many thanks and Happy MZ-ing in 2017!