Final answer:
Incorrect thread tension, dull blades, and improper threading can cause looper threads to break on a serger.
Step-by-step explanation:
The primary cause of looper threads breaking constantly when sewing on a serger can be incorrect thread tension. This occurs when the tension on the thread is either too tight or too loose, causing the threads to break. Another possible cause is dull blades, which can snag and fray the threads as they pass through the machine. Finally, if the thread is not properly threaded through the serger, it can lead to breakage. It is important to ensure that the thread is correctly threaded through all the necessary guides and tension disks.