Small Engines (Lawn Mowers, etc.): Problem with a Briggs and Stretton engine, rotary hand, key way

Question
Hi, I have a 4 year old Mountfield rotary hand-propelled mower powered by a Briggs and Stretton HP470 engine. The model number on the engine is 10D902, the type is 0141 81. 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


Answer
Mark
What you haver is a timing problem. Have you hit anything with this mower like a stump rod curb causing it to stop fast?
If you did you may have sheared a Key way on the flywheel. Check the center part of the flywheel by removing the center nut, Take the plug out when you do this and have some one hold the flywheel while you loosen it. If you have a access to air wrench you wouldn't need any one to hold it. Look at the key way to see if it is still aligned with the shaft.