Normally the small Briggs engines in the late 70s to early 80s will have suction fuel feed, while the larger ones had gravity feed. (Suction feed carburetors have the fuel tank screwed to the underside of the carburetor. Gravity feed carburetors have the fuel tank mounted higher than the carburetor, with a fuel hose from the bottom of the tank to the side of the carburetor.)
The suction feed carburetors from that period were VacuJet and PulsaJet. The PulsaPrime came later, replacing those earlier carburetors. If your vertical crankshaft engine from that period originally had a VacuJet, the third digit in the model number (if it is less than 10 cubic inches displacement) or the fourth digit (if it is 10 cubic inches or more) will be a 5. If it originally had a PulsaJet that digit will be a 9. (The first one or two digits of the model number are the displacement in cubic inches.) However someone may have swapped a PulsaJet for a VacuJet, or vice versa, at some time - the carburetor-and-fuel-tank units can be swapped as assemblies, though not individually due to differences in the fuel tanks to suit the carburetors.
The VacuJet carburetor has no fuel pump, so there is a simple gasket between the carburetor and the fuel tank. The PulsaJet (for a vertical crankshaft engine) has a rubberised cloth diaphragm between the carburetor and fuel tank. (Note that PulsaJets for horizontal crankshaft engines had the pump diaphragm mounted on the side of the carburetor, not between the carburetor and fuel tank. The PulsaPrime has this arrangement whether for vertical or horizontal crankshaft.) The diaphragm contains the main elements of the fuel pump: pumping diaphragm and flap valves. The pumping action is generated by intake suction pulses acting on the diaphragm.
The main variation in that 70s-80s period in the suction carburetors was in how the choke operated. There were three main variations: manual chokes, coupled chokes (such as Choke-a-matic) and automatic chokes. AFAIK you will find the automatic choke only on the third and fourth design generation engines. The design generation is the model number digit immediately after the engine displacement, and they started with zero, so if your model number begins with 92, it is a 9 cubic inch (148 cc) engine of the third design generation. AFAIK all 92 engines had automatic chokes, but I do not think the smaller or larger engines had them.
