Trapping Slag during Veritcal Up Stick

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I'm currently in welding school at Northrop Grumman, and because they've hired a LOT of welders recently their trying to get us in and out as fast as possible.  Due to this, I have really lacked development in my root passes, namely my vertical up butt welds.I'm stressing because I'm now on my x-ray plates which I can only do 4 then I wash out, and one practice piece in between that per position.  I am trapping small pockets of slag when doing my initial root pass (single weave, 1/8" 10718) and while my beads look good (free of undercut, porosity, rollover) I can see a tiny faint gray line, upon grinding into the weld bead I find a tiny pocket of slag, this will definitely fail an x-ray test.  I also seem to be making one end slightly higher than the other from time to time, though this isn't a huge deal. Short Version:  What commonly makes slag get trapped while welding vertical up?  How can I avoid trapping slag?Edit:  Single V-Groove Butt Weld with a backing strapLast edited by jonhendrix86; 01-10-2011 at 08:21 AM.
Reply:I think it helps to run as hot as you can possibly handle it. I think people have a tendency to run vertical up too cold, afraid it will fall on their feet! Believe it or not it is easier to run hot! Build a shelf, and take off!Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:So my instructor fooled around with my machine after I was still having issues, and found that it was changing amps up and down by itself!!!  And to think I did my overhead x-ray on this machine makes me nervous.  Also doesn't help that these machines have been in the school since the 70s......I got to change booths and did my vertical x-ray plate with no troubles at all, hope it comes back clean.  Thanks for the advice!
Reply:Also make sure your backing plate is as tight as possible to the test piece along the entire length of the weld.  Any gaps and your almost guaranteed to trap slag.Have we all gone mad?
Reply:Originally Posted by sn0border88Also make sure your backing plate is as tight as possible to the test piece along the entire length of the weld.  Any gaps and your almost guaranteed to trap slag.
Reply:When you say LONG ARC, is that too far away from the metal?