Two months ago I bought a 73 bb 4spd conv. It had been parked for 6 years and needed a lot of TLC. I've had one persistant problem I cann't figure out. The car will get starved for fuel (I think) erratically. It happens most often upon light acceleration from 30 mph to 50 mph. It doesn't seem to rear it's head when I'm accelerating from a stop. even giving the car a little gas to maintain speed going up a hill causes the problem. I can't get the problem to occur when the car is parked. I've tried running the car at 4000rpm for several minutes with the hood up to see what happens w/o any luck. While driving if it occurs it happens at the 2500-3000rpm range but dosn't seem to be dependant on rpm. Also when it occurs you can hear a "sucking/hissing" sound that get louder the more I press on the accelerator. If I lightly feather the pedal the car seems to slowly get fuel and run again. Also I can feel a strong pulse in the fuel line from the fuel pump working.
here is a list of what I've done. The distributor and plugs were because they were in dire need!

siphoned the old gas out.
rebuilt the carb (the power piston spring was missing in the old carb, thought I had the problem nailed when I found that)
replaced the fuel filters
new plugs
rebuilt the distributor.

What should I look at next?

 

Maybe try running a fuel pressure gauge that you can monitor while driving. If its not a fuel problem TO the carb than you may want to have the carb looked over by a professional. We have a member here on the forum who is great with carbs and distributors. His name is Lars and he is very knowledgeable and reasonable.