A system pumps are engine driven pumps, while the B system are electric.
Boeing says that a minimun of 760 KGs in tank 2 for GROUND operation of B pumps.
I would think that the same limitation would be on the A system, but when would you have the engines running, to provide A system pressure with less than 760 KGs in the # tank?
On the 737-300, the A system comproses the ENG 1 engine driven pump, and the ELEC 2 (Main Bus 2 powered) electric pump, while the B system comprises the ENG 2 engine driven pump, and the ELEC 1 (Main Bus 1 powered) electric pump. The manual requires 780 kgs
in the relevant tank for electric pump ground operation - as you wouldn't taxi or take off with the electric pumps turned, off that covers engine operation as well.
Is the 737-200 THAT different?