problem with mig 125...help?

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Hi, All,I have a century 125, have been practicing alot, and have been able to get some pretty nice looking beads. Was doing some work last night, welding some 0.100 wall square tubing to some grate that is about 1/8. Everything was going fine for about an hour then my wire started popping when I was trying to start a weld...the wire would contact the metal, burn up, contact again, burn up...i couldn't create a puddle.  I cleaned the gun, made sure there was no spatter in there. I didn't change any settings, the material is the same as when the welds were ok. Why on earth would this happen out of nowhere? The steel i was working with was nice and clean. It seemed like the wire was burning up too fast, so I turned up the speed from 6 to 7 (thats what the dial says, not sure about inches per minute or anything). max speed is 8. That didn't help. Then, I turned the heat down from 4 (max) to 3, and then my welds looked fine. My problem is two fold: how could this possibly happen without me changing anything?i'm working with 1/8" steel, which is the max thickness my welder can handle. shouldn't I have the heat at the highest setting? confused. any help is much appreciated. Thanks!
Reply:This sounds like the ground lead is not making good contact. I'd look at the clamp, and the wire itself to see if it is burned up. I am assuming you are running fluxcore wire, so I am not guessing gas issue, though it could be possible. Next thing to look to is the tip; is it really dirty?? Take a file and just kiss it to clean off the build-up. And, see that the tip is tight.Try this, and let us know what you find.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Thanks, I'll try cleaning the tip. Sorry forgot to mention, I am using solid wire with CO2/Argon. I already tried using it once when I forgot to turn the gas on, so I know what happens when you have no gas, and this problem didn't seem to act like that. The thing that gets me is that when I turned down the heat, the problem went away, but 30min earlier I was doing fine with the higher heat setting. Another thing I thought of...I put in a new roll of wire just before I started that day, and perhaps installed the drive wheel backwards? If I put it in backwards so that I'm using the .03 groove rather than the .024, maybe it started slipping after an hour? I will check the drive wheel and the pressure, then give 'er another go and see what happens.
Reply:another thing I thought of...my machine is supposed to handle .024 and .03 wire...if I was having trouble with the .024 wire burning up too quickly when using the highest heat setting, would it make sense to switch to the .03? thanks again.
Reply:maybe as time went on the piece you were working on got hotter and you didnt need the same heat as when it was cold..
Reply:Originally Posted by jonny ozanother thing I thought of...my machine is supposed to handle .024 and .03 wire...if I was having trouble with the .024 wire burning up too quickly when using the highest heat setting, would it make sense to switch to the .03? thanks again.
Reply:thanks Bert, that makes sense that the smaller wire got too hot. I realized that I should't have been using that skinny wire with the highest heat setting. I got some .03 wire, heat up, speed WAY down compared to what I had the .024 at, and it worked well. better penetration than the .024, of course, so I'm happy. thanks for the help guys!