If you're doing really small text I've found 3M Electrocut on the poly backer weeds great.
Like Stacy K said though you need to have your plotter set properly.
Handy tip when doing small text. Make a few extra lines and do the "rip off the band-aid" technique.
Get your weeding started so you have enough to pull back over itself.(180 degrees)
Hold down vinyl, take a deep breath and pull as fast as humanly possible while keeping a low angle on the material.
Laugh now, but once you try it you'll be sayin' Dang, that actually works.