whats the problem?

I have a Bolens 4.0hp push mower and Ive replaced the gas and replaced it with fresh gas, cleaned the air filter, checked the spark plug, checked the oil and I've even checked the starter and compression. But when starting it, it runs for a couple of seconds then it cuts off. I prime it 3x's and only when I prime it more than 3x's it seems to start but then again cuts off so whats the problem