Welding Tips and Tricks

Maybe some one can tell me what I'm doing wrong. Every time I try to TIG weld on 0.065 wall SQ Steel tubing, the weld seems to bubble up. I'm welding at around 90A, 15CFH Argon with 1/16 2% Thoriated rod.
I've cleaned the tubing to remove all the mill scale, but still the weld bubbles up. WTF? Do I need to purge the inside of the tube with Argon?

Thank you for your time.

That would be my first suggestion. Are the ends of the tube open or closed. Often times when you weld on tube that has closed ends, you will get a similar result from the heated air trying to escape out through the weld.