i mentioned this point because of my experience with my 1VJ. it has reduced fuel consumption about 1/2 l per 100 km.

try the following:
-completly drain the tank
-close both taps
-fill in 5 l on the left side of tank
-switch left tap to 'reserve'-position
-open the drain screw of the carb (bottom left) and let flow the fuel into a jerrycan (bike must be in upright position)
- after flow stopps check how much is left in the tank. this is the amount of fuel which cannot reach the carb without fuel pump. in 1VJ this amount is almost zero.

i cannot exactly tell you why the bike needs less fuel without fuel pump. probably it has something to do with its operating principle.

if you decide to keep the fuel pump, obey the 'golden fuel pump rule':
in the first second of recognizing fuel shortage FIRST close right tap, second switch left tap to 'reserve' position (and pray that engine don't stopps while a BMW is 1 m behind you on right lane of motorway ;-)

reason:
when switching to reserve position on left tap while right tap is open a certain amount of fuel will flow to the right side of the tank (principle of communicating tubes, remember your physics lessons?).
usually, on the first sign of fuel shortage the fuel pump has already sucked in air.
if the right tap is still open, the height difference between fuel level of tank and fuel pump is not big enough to press out the air from fuel pump.
what will happen then?
engine dies, of course.
and then?
no matter how long you press the start-button, the air will not be pumped out of the fuel pump unless you refill the tank.

so what's the conclusion?
-compared to xt600-models without fuel pump there is an extremly short time to switch to reserve. engine will die very suddenly if you don't obey the above rule. only possibility then is to make a short cut from tank to carb with a short piece of fuel tube overcoming the fuel pump.

considering the above, what is better?
-riding with a fuel reserve which you can't use (in the worst case)
or
-throw away the fuel pump and forget about a half l or so which you don't use?

your choise,
klaus