Been fighting with my Millermatic 185....

Metal is mild steel. Believe it is called "open metal", no rust/oil. Base metal is 3/16" mild steel, no rust/oil. Be welding along,beautiful looking bead, good penetration. Split second later open metal vaporizes, or weld gets really heavy looking, or very porse. Mig gin is same distance/angle. I also get a lot of burn back while trying to establish an arc. Like I mentioned earlier, seems like the feeder is pulsing slightly.
Going to take the machine apart today to see if everything is clean/tight. Will try to take a video with my phone as well.
I do have the feed tension cranked up quite a bit. Could this be part of the problem? Tension on spool is set so that it does not have a belly in it between the spool and feed wheels.