Rock the winder or handles back and forth to get the line to flow off them smoothly. Check your line lengths to make sure they're equal by attaching the flying ends of the lines to a tree or post and pulling on the straps or handles. With stunt handles, adjustments are made by winding the line around the line stop. With sleeved lines, untie the loops and slide the sleeving to the same location on both lines. Fold both lines at the center of the sleeving and retie identical loops.
Lines can stretch with use.
Check for equal lengths again after a few flights. If your stunt kite has snaps on the bridle lines, just attach them to the loops at the ends of your lines. Many kites terminate the bridles with knotted loops of line instead of swivels. First take the loop at the end of your flying line and form a loose lark's head knot. Then put the bridle loop through this lark's head.