I would go with the yamaha factory service publications. I have the archived tune up specs at home but I wont be back in the states until late tommorow night.
I set it at -4 retard it was at TDC1 motor starts alot better advanced and im at 29 deg advaced 25 didnt rev as high spark plugs look good like the motor is not running hot If you get a chance to see what the timing is both retard and advace let me but for now Ill leave it at TDC1 and 29 deg