Small Engines (Lawn Mowers, etc.): Briggs & Stratton will only run on choke, bolt torque, briggs stratton

Question
I have a Briggs 5hp model # 135202 on my Trac-Vac leaf shredding machine. It is a suction feed carb with no mixture adjustment capability. Every time I use it, the engine operates normally for a few minutes, them will only run with the choke on, often stalling out and needing restarting several times, until I am finished using it. I have had the carb apart several times, blowing it out with compressed air and carb cleaner. When reassembled the engine usually works fine for the first time I use it, and then it reverts back the same trouble again. Needing the choke on, suggests a lean condition. I am about at my wit's end dealing with this. I also replaced the spark plug and checked the gas cap for venting with no success. Can you please give me any direction on where to look to find and fix this problem?

Answer
How old is the engine?  The first 2 digets of the code number indicate the year.

How many hours are on the engine?

Is there a very fine screen on the short fuel tube?
 
Have you checked the head bolt torque?  Once had a leaking head bolt that I thought was the carb...did the same thing as yours...run a while, quit, run on choke.

Eric