Clint,

You're using an inverter machine. That's why I recommend the Lanthanated or Ceriated tungsten. The Sync is a transformer based squarewave machine. The Thoriated tungsten works fine for what Nails is working on.

Nails,

As Clint suggested, I suspect you possibly wicked a little of the puddle up on your tungsten. Won't be the first time, won't be the last, especially when welding like you are.

Your amp setting should be fine. I'm more familiar with the Sync 250 than I am with the 200 but shouldn't be much different. With your foot pedal all the way down, you should get the max amps dialed into the machine. As long as you're able to generate your puddle in 2-3 seconds your max setting is fine. You'll want to back off from there as heat builds in the puddle. Since you've got pulse capability on your sync you could use that to help freeze the puddle, but I think that's opening a whole new bag of tricks. You'll need to play with some similar gauge scrap to get a feel for your own pulse settings and what works for you. The thing you need to keep in mind, you're not doing a structural weld where penetration is all inportant, you're trying to minimize the heat while still maintaining a molten puddle. It's a fine line between the two. As you work at feeding the filler and backing off on the amps you'll hit that sweet spot where you just "know it's right". In doing that vertical fill (firewall) you'll find that you want to use about 25-30% fewer amps than you would if you were filling a hole in material "in position".

Keep us posted on your progress. Sounds like you're making great headway.

PS. Sounds like you're now getting things dialed in. If it makes any sense, I'd just say that you want to use your arc to chase that filler around the circumference of the hole.