FIXED: Pressure back through intake

I have a 2011 John Deere D100 with a Briggs and Stratton single cylinder OHV engine.  Engine model 31P677.  Last year I replaced the camshaft due to a broken decompression cam.  It has about 40 hours on it since.  When cutting the lawn yesterday the engine ran fine for about an hour then suddenly lost power.  Now it won't stay running.  Here is what I have done so far.
 
replaced spark plug
drained carb and fuel tank, refilled with fresh fuel.
Compression, 155psi
spark is very strong
Valve lash is ok.
 
When the engine is cranking over by the starter I get pulses of air back through the carburetor.  I disconnected the intake manifold from the head and while cranking I get pulsed of air out through the intake port.  I know that should not be happening. It should be vacuum. I removed the cylinder head and the head gasket doesn't look bad.  At least is isn't too obvious.
 
I filled the cylinder head chamber with gas to see if the valves were leaking and no fuel leaked though.  I didn't expect it to with such good compression.  I will be putting it back together over the weekend.  Does anyone have any ideas on why I would be getting pressure pulses back through the intake?

The starting compression should not be anywhere near 155 psi if the ACR is working. More like 70-90 psi. So check for the ACR bump on the intake valve.
 
I kinda expect a bad (loose) valve seat; although, a little back pressure in the intake during starting is normal.  It will not leak with the head off the engine as the springs will hold it sealed. I had several over the years that would seat and unseat while running. Matter of fact I just got though replacing a head and piston on a 31Q where the exhaust seat was doing this until it finally shattered. It also didn't help that the engine also had a blown head gasket between the cylinder and push rod galley.

Check for a sheared flywheel key.

I believe my date code is  March 31, 2011.  I have attached a picture of the valve cover.