1) check the oil level make sure it is FULL but not overfull.
2) when it stops spray some starter fluid down the carb & crank.
Engine starts = fuel delivery problem
3) get a red neon in line spark tester
When the engine dies hook it up and check for a spark when cranking
no spark = bad magneto or defective safety switch wiring
4) remove the blower housing and take the small wire off the coil
Crank engine
No spark = defective magneto coil
spark = defective wiring