Small Engines (Lawn Mowers, etc.): Trouble Starting Lawn Mower, briggs and stratton, head gasket

Question
I own a Power Pro self propelled lawn mower equipped with a 5.5HP Briggs and Stratton Quantum engine (129802-0894-01-9509195).  The mower has never burned any oil and does almost everything I want.  I’ve owned the unit for over five years and received it from a relative, who could never start the mower, which is probably 15 years old.  If you start the mower with a little shot of ether directly through the spark plug chamber it starts on the second pull.  If you prime and choke the carburetor it won’t even cough.  If you spray ether into the carburetor after removing the two air filters it will not start.  If you shut the engine off after it’s been running it will not restart without ether.  
I took another carburetor, primer bulb and filter housing from a perfectly working (it actually is a bit of an oil burner) 6HP Briggs and Stratton Diamond engine (12J802-2815-01-97021468) and swapped it out and the problem still exists.  I use the mower only as a trimmer and it probably gets 10-15 hours of usage a year.  I’m just curious what you think is the problem.


Answer
Have you checked the valve clearances?  Is the intake pipe broke/cracked or is the intake gasket leaking?

With the air filter housing removed exposing the carb, with the engine start if you place your palm of your hand over the carb throat?  Basically you are cutting off all air forcing the engine to pull full into the intake system.

Is the head gasket leaking?  Do you have a cylinder leak down tester?

Let me know.
Eric