Have you used this wire successfully before? Have you tried a different spool of wire? Has the wire developed some corrosion on the surface? Could the wire be out of spec.
I bought a Millermatic 185 over 25 years ago (also with a spool gun) and it's still going strong. One thing about higher quality welding machines of yesteryear is that they're better able to deal with all that life throws at them. My welder lives in an unheated garage that can be -20°F in the winter and 90°F in the summer and yet it still works whenever I need it to. The duty cycle is great too, but most hobbyists aren't going to worry much about that.I bought my Miller MIG 25 years ago with a spool gun. It's still very good. At the time, two of the advantages were the spool gun and duty cycle that stomped most of the machines at the time. Sure, it was a bit more, but it's still going strong at 25.
However, technology has changed over 25 years. The difference in quality probably is a lot less than it was 25 years ago.