The air/fuel mixture screws are usually capped off and the adjustment might not be possible, but if the air/fuel mixture screws are exposed then turning them in will lean out the fuel mixture, and turning the air/fuel mixture screws out will en-rich the fuel mixture.
With the engine fully warmed up and at normal idle speed adjust the air/fuel mixture screws one at a time, and turn each air/fuel mixture screw in until the engine just begins to mis-fire, then back out the air/fuel mixture screw one and a half turns to two turns to achieve a smooth idle.
Be certain that the air and fuel filter(s) are not plugged up (there might be a fuel filter inside of the fuel pump as well as the fuel filter/stone at the fuel inlet to the carburetor) and keep in mind that the minimum octane requirement for that engine is 91 octane, and 92 octane is the average octane rating for the premium higher grade fuel, so a bottle of octane booster added to a full tank of fuel will greatly improve the way the engine idles and performs.
That engine should have an electronic HEI (High Energy Ignition) distributor with the large distributor cap and with the ignition coil inside of the top of the distributor cap, and keep the tune-up parts in good condition and replace them when they wear out. The tune parts would consist of the distributor cap, ignition rotor, spark plugs, spark plug wires, and the spark plugs should be gapped at .045 in.
For better performance from your El Dorado a 1 inch spacer under the carburetor will really help a lot if the hood clearance will allow it, and you will need to set the ignition timing to 10 degrees before top dead center, and adjust the accelerator pump on the carburetor for maximun pump efficiency so that as soon as the throttle is opened there is two healthy squirts of fuel from the accelerator pump, and they should squirt as soon as the throttle is opened, and if the throttle can be opened and the accelerator pump does not squirt fuel at the same time as the throttle is opened, then there will be a lag or stumble from the engine on take-off and a severe loss of engine performance. (The accelerator pump must pump fuel into the carburetor at the exact same time as the throttle is opened)
For better performance check the adjustment of the secondary throttle linkage, and let me know if you require assistance with any of the proceedures.
Be sure that the vacuum lines to the EGR valve are correctly routed and that the EGR valve is not operating at idle.
Also, that engine has a plastic timing gear that was used for the camshft timing gear, and I would seriously suggest that it is changed before trying to get any performance from that engine.
Other than those modifications, the engine would need a better camshaft and the catalytic converter removed to increase the performance of that engine.
Here are some images to help assist you.
Fuel Pump Filter:
Rochester Carburetor Secondary Adjustment: