I just bought a 1990 zzr 400 x and cant find much info on it.Are they very common?also it doesnt run very smoothly.when you start it it takes a long while before you can rev it past 5 grand ,to long for it to just be a cold engine,also once its all going good it goes to about 5-6 grand then starts missing till about 9-10 grand.any thoughts?the guy who owned it before me recond one of the carbs might need a rebuild.