Mower coughs and splutters starts briefly then dies

Remove the gas and replace with new gas...take the carb apart drop the bopwl and clean out spray all the holes inside carb with carb cleaner and use a pin needle to prod all the small orifices to clear em....pull the plug and clean it check the oil level...spray off the grease ***** on the kill switch on the side of the motor block... be sure the blade isnt bent or loose...try it you'll like it!!
If it pulls your arm out of socket...pull off the recoil housing and rcheck the keyway shaft key for being broken or worn....remove the flywheel to replace it by removing the 3/4 " nut and tapping the flywheel gently while pulling flywheel upwards or use a puller, once off take the key to local hardware store and replace it for 50 cents...reinstall....start it up.....you'll like it I guarantee it!!!