Lawn mowers.. Sears 6.5 hp 22 inch mulching?

I have a lawn mower that won't stay running for more than 15-20 seconds. I think it's just running off of the primer.. If the fuel line was clogged, would it still feed the primer? Also, if it was the spark-plug, would it even start? Is it a carb ploblem? I can't figure it out???? Help please!