How can i get my Briggs And Stratton engined mower to start?

Hi, I have a 4 year old Mountfield rotary self-propelled mower powered by a Briggs and Stretton HP470 engine. The model number on the engine is 10D902. I cannot get it to start, so far i have emptied the old fuel and oil and replaced with new, removed the air filter, cleaned and soaked it in engine oil then wrapped it in a cloth and squeezed until no more oil came out, cleaned the spark plug with a wire brush, put it all back together again. It now will not start. When i pull on the cord it recoils back so fiercly it felt like i'd broken my hand. With the spark plug out, when i pull on the cord it feels smooth, with the spark plug in it doesn't. I left the spark plug out pulled on the cord a few times and i've left the spark plug out for over a hour thinking i'd flooded the engine, but still no difference.
Any help appreciated