California Nissan 720 z24. Having trouble with the truck running rich, no vacuum leaks, new CAT, and new plugs/wires/rotor. Had the carburetor rebuilt, guy at the carb shop said it could be an issue with the ECM. I checked under the driver seat to see if the green light was on while the truck was running but it wasn’t. The light on the ECM only goes on before the truck starts and goes off while it’s running. Does anyone have any information on how the carburetor runs off the ECM and or how to tell if the ECM is bad?

Thanks