Gravity vs Pump Feed

[Joe Godec]

Does anyone know why the needle and seat are different for briggs gravity feed vs pump feed. Can you use one on the other for example use the (pump feed) brass seat style with gravity gas tank?
There has got to be a reason why they have both.

 

[StarTech]

It has to do with amount pressure the fuel in under. Gravity is very low pressure so the seat opening need to be larger with a matching needle. Fuel pump systems are under up to 10 psi so a smaller opening in the seat allows the float and needle to have more mechanical advantage over the fuel pressure. It is like you going out in a high wind day and holding a sheet of plywood sideways vs a 2x4.