I have a generator that has 240v the plug for it is 4wires I want to hook up my 220v welder to my gen but my welder only has a 3wire plug I'am trying to make a pig tail so I can hook them up together can anyone help me thank you

What is the plug configuration of the welder (NEMA)? It's likely that your welder uses two hots and a ground rather than a neutral. You need to determine that before you omit one or the other.