I have a Craftsman Lawn Tractor Model 917.252520. When the motor starts and runs for a few seconds fuel and oil pushes out of a vent tube that houses the air filter and drowns out the motor. Tried replacing the carb but no changes.

Sounds like the motor went bad. Either the rings went bad and its bypassing the pressue into the crank case or its also possible that you have a bad set of valves.

Hi,
Could simply have gas in the oil overfilling the crankcase and causing a pressure problem.
Peace,
Clarke