3.5hp briggs question-----carb????

I have an old pushmower with a briggs engine, model 92902,type1982 01. I have replaced the diaphragm for the carb. and still have the same issue. it will only run if I hold the throttle wide open. it will not run even at half throttle. I have the throttle cable unhooked and am operating the throttle shaft with my finger. any ideas what to do next. thanks in advance