I also piece on a Viking Mega Quilter - same machine. You have to turn the top tension knob a lot to make a difference - not like a coputerized machine where just a little turn changes it. also the pre-tension knob (above the regular tension discs) should be about 1/4" apart. and you cant be afraid to change the bobbin tension. Get a spare bobbin case if you're afraid of screwing it up. Look at Jamie Wallen's you tube video on adjusting bobbin tension - same as they do on longarms. these machines are incredible workhorses!! Have had mine for 13 years & it still makes a beautiful stitch.