Ricks Motorsport Electrics offers 2 and 4 brush replacement sets for Mitsuba and Nippon Denso starter motors. You will need to solder or spot weld these brush sets onto your plate.
Fitment:
1986 Yamaha YFM225 Moto-4
1988 Yamaha YFM225 Moto-4
1989 Yamaha YFM250 Moto-4
1990 Yamaha YFM250 Moto-4
1991 Yamaha YFM250 Moto-4