Hey, I had the same problem since I bought the Jeep weber carb for the 4.2L,
After hard hours of tuning, finaly got it running smoothly.
My carb is not conected to anything, just The vacumm line to he distributor (advance).
Things to take care of:
a) Check any vacuum hoses
b) Install a Fuel Line return to the Fuel Tank, this will take any excess of fuel to the tank.
c) check for the correct Chiclers fo low and high rpm, had to change the lower, to much fuel was going through.
d) clean every port in carburator, the smallest dirt can cause to work bad.
After a lot of trial and error. finaly is running smooth.