Why doesnt my 1979 rm 250 start?

I baught a 1979 rm 250, the previous owner told me that he had put a new cdi,clutch,bearings,seals,and spark plug. after he had that put in the motorcycle it still wouldnt start so he sat it for 2 years and thats when i baught it from him. I checked the spark plug and oil, and even cleaned the carb and it still wont start..it does have a spak though...can somebody please help me out with some advice? thanks....