Start out with a brand new needle.
Be sure the machine is threaded properly. Also, the presser foot MUST be raised before threading so the thread will seat properly in the tension disk.
The standard setting for the upper tension is the midway point between the high and low number.
If the bobbin thread is still way too loose, you can try adjusting (tightening) the bobbin case tension. If that does not fix the problem, you can probably try purchasing a new bobbin case for your machine as the old one may be broken or worn.
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