i have a 77 or 78 yz400 not sure exactly with a mikuni , the jet needle has been broke and i cant find anyone who knows what size the stock needle is, they all tell me they dont have parts for a bike that old.. the number on the needle is not there because its been broke off.. my clymer manual says it takes a 6f16 or 6f8.. can i cross reference these numbers to a newer needle or will it have to be specifficaly a 6f8 or 16?. if so where can i ifnd this needle?