I got an belarus 800(same as yours but 2 w dr)for more than 20 yrs.
I dont know what problems you have?, please post them,i can help.
I changed mine to 24V starting by putting a paralel switch in(can be had from a belarus dealer cheaper than anywhere else)Keep the 12 v starter cause it'll spin faster that way and applying 24v wont hurt it as i have used the same starter for over 15 yrs,wheras i burned out a starter a year prior to converting.
If the starter drive over ride clutch goes belly up(happens often),just weld the gear to the housing and it'll last forever.
Hope this helps.