The motors I spoke of where from the mid 90's.The first GP set up from Yamaha as I remember was a 250 CC with 120 Ponies. I worked for a Yamaha dealer in the sixties. We had a works bike on display for awhile. It definitely was a rotary valve. I think it red lined at 24 K. I can not not imagine what it could have lacked except a super man rider. Very light plenty of aluminum with duel disks in the front and a gigantic disk in the back. I was not allowed to tinker with it but tried anyway. Thanks