about fuel pumps

I have a mechanical feul pump. I have SU's with shaved needles and they are bored out to 50mm. I was told by Rebello that the mechanical fuel pump would be sufficient enough, but at high RPMS, it hesitates, like it needs more feul. there is never any smoke coming out the tail pipe, and If I back off the throttle a little, then punch it again, and I can take it up to the red. My rotor is a little worn, but it feels like a fuel issue. Anyone have any comments??? What kind of psi difference is there between the mechanical pump and the electric. I looked by my feul tank and notice a couple of wires that look like they could be used for the power for an electric feul pump( the wire harness has 4 leads, 2 to the tank and 2 attached to nothing. Is this correct, or was the 1973 the only 240Z that had the extra power leads for an electric fuel pump.