craftsman riding lawn mower model 917.272350 is hard to start?

I have a craftsman riding lawn mower model 917.272350.with a 15.5hp Briggs and Stratton with 42" deck.The only way I am able to get it started is to raise the hood and rotate the flywheel so that the piston is in the bottom of the cylinder.When I turn the key it turns over and stops when the piston reaches the top of the cylinder.I dothis several times then all of a sudden it starts right up and runs great.I removed the spark plug and it turned over continuosly like it should.It seems like it has to much compression to turn over .It has a brand new battery in it .Please let me know what you think I should do to correct this problem. Thank you.

David
June 2008