mower getting intermittent spark?

I have a troy-bilt mower with a 5.5HP tecumseh motor, at least i think its 5.5HP. Its running like its getting intermittent spark then it shuts off and will not start again for a long period of time. then as expected it will run for several minutes just fine and then it act like intermittent spark and eventually die again. any ideas? all advice will be greatly appreciated.