My 48 does this once in a great while. It will run great until the fuel in the bowl of the carb runs out and it will die. Crank and crank with no start. Tap on the side of the carb a few times to get the float to unstick and release the needle and seat and she'll fire in a few minutes, after to bowl refills.
It's done it to me twice, once along side of the road and once down in the woods hauling firewood up to the house. I decided to diagnose it the second time it happened. Found the ignition system working fine so I primed it with some gas and it fired. The fuel filter was still full so I thumped the carb with a soft faced mallot and it fixed it.
Hope that all that's wrong with yours,
Scott
