The reason why the thread is always looping under the sewing machine

In most cases, the problem of sewing machine needles can be solved by the following methods: First, check whether the installation of the sewing machine needles is reasonable. If there is no problem, replace the new needles for a test run. If it still cannot be solved, it may be that the rotary hook is not running well or the rotary hook has burrs. , it can be recovered after processing.