Yamaha 8B 677 1977 model need help adjusting the carburetor air/fuel mixture screw

[Chriserrr]

Hey i’m having a hard time adjusting the air/fuel mi ture screw i already cleaned the carb and the main jet and pilot jet and fuel filter and lines so i know its not a dirty carb it backfires when i rev it and i just tried to adjust it in and out couple of turns each way and it still misfires with new plugs also. Please help I’m lost its a 8hp 2 stroke Yamaha 8B 677 year 1977