1982 Chevy El Camino carburetor issue

The car had been sitting since 2012. I recently
obtained it and started working on it. I got it to run.
It passed inspection however it has no power. It has
the 3.8L v6. When I floor it, it tries to shut off. I
thought maybe fuel filter so I heckled.  The fuel filter
was in bad shape so I replaced it.  The car still tried
to shut off.  I started tinkering around with the carb
and adjusted he middle screw on the top of the
carb.  Now the car won't idle no matter what
position I turn that screw.  It is now hard to start as
well.  What is that screw on the very top near the
center front of the carb for?  I pulled it out and fount
it had a spring loaded shaft that had holes in it. I am
assuming this adjusts the idle fuel mixture. The only
reason I touched it was to chase down what jets are
clogging up causing the car to shut off when under
a load such as flooring it while in drive. Any
suggestions would be greatly appreciated.