1997 Nissan Pickup runs rough, floods

runs rough and floods after warmup.

Guessing you have a carburetor, time for a rebuild or replace.

One thing to check is a faulty coolant temp sensor for the computer.

If this sensor keeps telling the computer that the engine never reaches operating temperature when it actually does, it can cause the problem you’re having.

Tester

In addition to @Tester’s advice, I’d also recommend a check of the fuel pressure in the fuel rail and the possibility of a leaking injector.