The most common reason for thread pull outs on embroidery machines is improper tension. Look at the back of the design and you can determine this by the ratio of upper thread and bobbin thread showing in the back of the design. For instance, if on the back of the design you see little bobbin thread showing, then either your bobbin is too tight or the top tension is too loose. Make sure that you have an inch to an inch and a half drop to the bobbin. If the bobbin drop test looks good then tighten up the top tension. Remember whenever you turn the tension knobs always provide a good balance by turning both the small and the larger tension knobs to reach the desired look.
The next possibility is the picker not working correctly. The picker is that forked component just outside the bobbin area of your machine. The way the picker works, is every time the machine starts to sew after a trim has occurred, is on the first few stitches it moves into the bobbin area and the 2 prongs of the picker align the bobbin thread so that it is straight, so that when the upper thread gets picked up by the rotary hook that it meets the bobbin precisely to get a good tie in for the first few stitches during the inching mode.
The inching mode is those first few stitches that the machine makes at a slow speed just before going to the normal embroidery speed. It is possible that the picker on your machine may be slightly out of adjustment. To check to see, push the picker in as far as it goes and ensure that the picker arm (the part that has the two prongs on it) is straight. As you push it in towards the bobbin, use the thin black support bracket that will be just above the picker after you pushed it in about halfway towards the bobbin. Use this thin black support bracket as a straight edge to determine if the picker arm is bent or twisted. If it is, gently bend it back into shape.
The next thing to look for is as it passes under that support bracket; make sure that the picker arm does not contact the screw that secures that thin black support bracket on the left side. Often times as the picker arm fires into the bobbin area, it makes contact with that black screw head causing it to stick a bit and not allow the prongs to gently press up against the cardboard side of the bobbin. I forgot to mention that when the picker fires into the bobbin area, not only does it help align the bobbin thread for proper connectivity, but the prongs gently push up against the card board side of the bobbin to prohibit the bobbin from moving too much as the two threads (upper and bobbin) meet. If you do see that it is sticking then loosen up the two small Phillips screws on the left side of the picker arm and lower it slightly so that it misses that black screw.
Another thing to check as you press the picker in the rest of the way is to see how the pig tail of the bobbin sits in between the two prongs of the picker. It should be dead center in the middle of those two prongs. Again if it does not then loosen the 2 small Phillip screws on the left side of the picker, motion the picker slowly pass the black screw ensuring that it does not make contact, check the straightness of the arm using the support bracket as a straight edge then go the rest of the way in and manipulate the picker so that it divides the pigtail. Hold it there and re-tighten the screws.
The next possibility is that the AUTO BACKTACK setting is not set correctly in the machines settings. To check for this do the following.
For LCD type control panels (the type that displays the image of the design you are embroidering) do this:
1) Press the SETTING button.
2) Scroll down to EMB PARAMETERS.
3) And find the AUTO BACK TACK SETTING and make sure that it is set to ALL.
For LED Type systems (where no image of the design is shown,just alpha-numeric information) do the following:
1) Press the MACHINE button.
2) Select the EMBROIDERY FUNCTION and press SET.
3) Locate the AUTOBACKTACK SETTING and ensure that it is set to ALL.
You will have to press a number that corresponds to ALL, on the LCD Type screens you will clearly see the number you need to push to select ALL. On the LED type screens you will see that the ALL setting is usually defined by the letter "A". I believe that you will need to press the number 3 to make the setting set to ALL for both styles of control panels.
If all of these things are set correctly than we can probably cheat a bit as it may be the lettering you are sewing is not created in a way to help the machine provide good connectivity. I mentioned earlier about the inching mode the embroidery machine does before it picks up speed, there are 2 like inching modes that every machine does.
When the machine first starts a design, it does inching mode, and it also does inching mode after every trim as the machine starts to embroider again. We can change the value of both the AFTER TRIM INCHING STITCH, and the INCHING STITCH to a higher value to better our chances of getting that connectivity during these modes.
These settings can be found here:
For LCD type control panels:
1) Press the SETTING button.
2) Scroll down and select M/C PARAMETERS and press SET.
3) Locate the AFTER TRIM INCHING STITCH and set it to 4 st.
4) Go to the next screen by pressing NEXT and find the INCHING STITCH setting, and set it to 3.
5) Go to the next screen and look for PICKER OFF TIMING, set it to 40
The picker off timing will controls how long the picker stays into the bobbin area, which controls the amount of tail that is left after a trim. The theory here is that making the tail a bit longer will increase the likelihood of disallowing the thread to pull out on inching mode. But be aware that you may have thread tails too long that drag across the embroidery area that you will need to clean up after the design is finished. If this is the case set the PICKER OFF TIMING to a lower number.
The final thing I would like you to do is to test the picker to see if it is sticking or if it is firing properly.
On LCD Type control panel, do the following.
1) Press the TOOLS button.
2) Scroll down to MACHINE and press SET.
3) Select MACHINE TEST and press SET.
4) From the selection shown scroll down to PICKER TEST and press the SET button.
Every time you press the SET button the picker will fire into the bobbin area. Watch the picker as it fires in and see if it sticks or if it works properly, or if you still need to make another adjustment. Press the SET button several times to ensure the proper workability of the picker after you've made any adjustments.
For LED type control panel do the following:
1) Press the M-SETTING button.
2) Select the MACHINE TEST option.
3) Press the SET button.
4) To make the machine test the picker you will need to press the START button.
Press it several times to test that picker and to make sure it is working properly. If by some reason during these tests that you do not see the picker firing at all then your problem would be the picker solenoid is broke and needs to be replaced.