I have a toro wheel horse riding lawn mower model# 71185;?

how can i stop the gas from filling up an running over in the carb. i have gas in my oil an i have took the bowl off the carb an cleaned the float thinking it was the float sticking. the mower has been sittin for a year. any advice would be really helpful thanks. the motor is a 13 h.p briggs& stratton engine # 28m707-0122-01 an code #9702062B