What causes my engine to sputter & backfire after starting it?? HELP!!!! on 2002 Dodge Dakota

I just rebuilt the engine and now it turns over and starts but, after running a few seconds, it starts to sputter & back fire. I put it on a hand held computer to diagnose it everything checked out no codes were given all it said was it was 15 degrees advanced I need a little help here

Asked by for the 2002 Dodge Dakota