Need help starting my 3.5 hp Briggs and Stratton lawn mower motor?

I primed it a couple of weeks ago and I thought I flooded it. I have to keep pulling the cord out and sometimes it starts but only for about a second. I keep playing around with the choke as well. It doesn't seem to want to start. Changed the spark plug at the beginning of last summer, but the motor is catching so I don't think that is what it is. Need help. Thanks in advance.