B&S starts first pull, but won't start again after shutting off (new carb)

Hi.  I've got a mower with a Briggs & Stratton engine I picked up from someone throwing it away because it wouldn't stay running (can't find the HP or model number anywhere).  I cleaned the carb twice with no success, so I just bought a new carburetor and spark plug.  Thing started right up first pull.  However, first time I used it, it did start right up again, first pull, used it a while, then shut it off to move a chair, and it wouldn't start again.  Took off the air cleaner and sprayed some starting fluid, and after a few pulls, it started again.  Running like a champ.  Until I stop again.  Seems if I wait a day, it'll start up on the first pull again.  Definitely seems to be a fuel issue.  Air lock?  As I mentioned, it's a brand new carburetor.  Thanks for any advice!

Hi,
Unfortunately, there isn't even a choke on this machine.  I've tried to add a couple photos, but that doesn't seem to be working.  Anyway, no choke.  
 


 

Hi.  The carb is not black plastic.  As for the choke, I thought you meant a lever or something external that controlled the choke.  It's just automatic, which is a pain.  I'll check the head bolts.  Thanks for the reply and suggestions!