1986 trx250x jetting help please

I have a 1986 trx250x I bought that I bored .040 over and out a 12:1 wiseco piston in it I currently am running stock exhaust until I can afford aftermarket I am also running 50/50 110 octane and 93 Idk of that matter it currently has a 125 main jet and runs quite lean can somebody help me with a starting point please