how can i fix my westwood mower?

I have a1995 t1800 westwood mower which has just developed a starting problem.it fires on the turn of the key but fails to run.if i try to start it again it wont fire at all unless i leave it for a good 5 minutes.there is no problem with the fuel delivery and both plugs seem to be sparking ok.any suggestions? its a briggs and stratton model number 350777

paul
May 2012