B737NG engine start

[zth]

Hello All,

I have a question regarding engine start procedures on the 737NG series aircraft. Specifically I'm interested in what are
a) the minimum requirements (technologically speaking)
b) operational requirements
for fuel quantity in the center tank to complete engine start?

As far as I know, the engines are normally pressure fed from the center tank, unless it's quantity decreases to near 0; and are then normally fed from the respective main tanks. I'm aware of operational procedures restricting center tank pumps to be switched off at the various minimum center tank fuel levels for the various phases of flight; I'm more interested to know are there any limitations both a) and b)-wise regarding engine start with center tanks empty?

Thanks for your input!

Regards,
Zoltan Hegedus