Originally Posted by John_M_

Right, the pump diaphragm has the return spring on one side of the diaphram, along with the flapper check valves, that's part of the pump section to draw fuel from the tank to feed the metering section... the pump pulse is ported internally through the venturi throat... where it differes greatly from the walbro, if you look at the carb exploded view in the 41ts pdf, you'll see the 4 button / disc valves between each of the fuel metering stages... from what I gather, those button/ disc valves come as part of the complete carb assembly, or as part of the fuel pump subassembly... they function similar to the walbro needle & seat... when those button valves start to leak, fuel will drip from the venturi and the engine will run erratic, not hold a tune.