How exactly does a sun set? How exactly does a posi-trac rear-end on a Plymouth work? It just does.
Every Briggs "Pulsa-Jet" carburetor has a diaphragm fuel pump no matter the size of tank, the only difference is the length of the pickup tube. In the picture below referencing the "Pulsa-Jet" carburetor for a 3.5 Briggs model 091212 with 1qt. SHALLOW tank, you'll see three parts circled in red. There's the diaphragm, spring and the little metal ring that keeps the sharp part of the spring from tearing the diaphragm. As the piston travels down for the intake stroke and the intake valve opens, air flows through the carburetor. This air creates a suction or vacuum, one that works against the spring in the diaphragm PUMP. Once the intake valve is closed, there's no longer any suction/vacuum and the spring returns the diaphragm to it's "rest" position". This back and forth motion of the diaphragm IS THE PUMP!. The two little "U" shapes (yellow arrow) in the diaphragm are the pumps "valves", one coming from the tank, the other to the internals of the carburetor. If the diaphragm or spring is damaged, it won't pump fuel. I have also included pictures of the parts, part numbers and their descriptions.
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I am puzzled why you are talking about the pulsa-jet and not the carburetor that the original poster has. Your statement that every single pulsa-jet has a diaphragm is correct, but has nothing to do with the original engine/carb in question.
So no one is confused, THE CARB IN THE ORIGIONAL POSTER HAS ON HIS ENGINE DOES NOT USE A FUEL PUMP!