On the `72 CB500 I run the same size front tire and a 120/90/18 on the rear, and that sounds about right.
4000 rpm on these motors is nothing because thats not even halfway to redline,they don`t start making real power until after 6000 rpm.
That`s what makes these bikes such a blast to ride
17 front and 34 tooth rear are stock.
You can run an 18 tooth up front but don`t let the chain get too loose because it`ll shear off the clutch actuater rod.
Ask me how I know