The idle screw is up by the recoil safety. Sounds like you need to do a link and sync> Did you verify fuel is squirting out of the primer hole in the carb?
Is the primer working? When the square Knob is pulled out all the way does the wire pull on the magneto? Is the idle screw set correctly? That Is on the recoil safety.
Your engine has been working like that since 1988 and still running strong. Why the change now? What about the bottom 2 cylinders that get VERY LITTLE oil when idling? I think you are overthinking this.