My experience has been that a flooded N will, more often than not, not start by giving it full throttle.
I've never had to do this (I walk away and try a few hours later), but many suggest putting new plugs in when it floods. Autolite 437 gapped at 0.025" are recommended.
Overall, it sounds to me to be an electrical issue. I would re-set the points and make sure all of your electrical connections are clean and tight for the season.
As Stephen and Royse have said, be sure to shut the fuel off when the tractor is not running. Make sure that you change the oil before running this season too! - you guessed right - that leaky gas had to go somewhere.