Small Engines (Lawn Mowers, etc.): B&S MTD will not keep running, carburator, time gas

Question
I have a MTD model 12A-526L062 lawn mower.  It has a Briggs Quantum motor 120802. I am having problems keeping the motor running.  I will prime it and it starts but dies right away.  I have taken the carburetor apart checked the float and inlet needle cleaned really well and it is getting good fuel flow to the carb. I cleaned the jet and it is clear. If I pump the primer bulb it will keep running.  Is there some type of fuel pump on these engines?  If so how does it work?  How does it pump the fuel into the engine?  

Answer
 Hello Ken:

 The Carburator Needs to be Soaked Overnight in Cleaning Solution. Over Time Gas Forms a Varnish. This Varnish Clogs the Ports and Passages Inside the Carburator that Feed gas to the Jet. Without Soaking the Carburator the Varnish Still Restricts the Gas to the Jet. Once the Carburator has Been Soaked, Blow Out All the Ports and Passages with Compressed Air. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John