having trouble with my gillera runner 125 sp ,?

Hi im having trouble with my gillera runner 125 sp it seems to be running funny but i dont now whats causing it or why basicly it will run fine and ill leave it for an hour and somtimes it will blow the plug and they dont seem to work again so i am forever changing plugs and i am using the right ones i get them from my main dealer . I would appreciate any help as i cant find any any were !
1 whats making my bike run funny and blowing plugs ?