Proper threading, both on top and inside the machine, is required for a sewing machine to make strong, even stitches. The top thread is out in the open, making it simpler to spot top-threading errors, while the bobbin thread takes more investigation to correct when there is a problem. An improperly loaded Juki TL-98Q sewing machine bobbin causes missed stitches and weak, loopy stitches. An improperly loaded bobbin also causes the bobbin to back-spin, making a potentially damaging knot of thread inside the bobbin case.
Depress the power button to turn the sewing machine off.
Raise the needle to its highest position either by turning the hand crank on the side or by pressing the needle up/down switch located on the front of the machine.
Open the hinged side plate to expose the hook and bobbin case by lifting up on the outer edge. The side plate is located on the base of the sewing machine, about an inch to the left of the throat plate where the needle goes into the base.
Lift the lever on the bobbin case and pull the bobbin case straight out to remove the old bobbin.
Position the full bobbin in front of the bobbin case so it turns clockwise when you pull the loose thread end.
Slide the thread end into the slot in the edge of the bobbin case, and continue sliding the thread upward until it slips under the tension spring on the bobbin case. Pull at least 5 inches of the thread end out.
Hold the bobbin case by the latch, and slide it straight into the hook. Release the latch, then close the side plate. Press the needle up/down switch two times to draw the bobbin thread out of the hook.