Almost the last piece to go back on the engine is the fuel lift pump. This mechanical pump is driven by a special lobe on the cam shaft, causing the actuator to lift a diapragm thus drawing fuel from the tank and sending it on its way to the carb. There is also a small priming lever beneath…. the only reason for which is to test the pump is working should there be a need to eliminate it fault finding…. I think
The glass jar is there to catch any sediment that might have gotten through the 2 previous gauze filters.