Neil on one of the Facebook groups recently shared this fantastically helpful info:
Here is a very useful guide on checking your machine needles for a Japanese machine
The full needle test is as follows and hope this helps as most of the issues with a machine can be the needles
Remove the sponge bar and bring all the needles forward to the hold position and then pushing down at the latch end so the butt of the needles lifts up run you finger slowly across the who bed so every needle lifts up and returns down, any that dont drop bsck down or look bent remove these as they are faulty.
Then put all the remaining needles back and replace the sponge bar.
Now you bring all the needles forward into hold position and look for any that are not straight any needles you see that are not return to out of work position ready to remove them when this testing is finished
Then use a piece of paper to run across the machine and open every latch
Place your finger on the open latches and run it across the whole needle bed applying slight pressure to force the latch open.
Then using the paper close every latch, if a latch wont close or is stiff return in to the non working position ready to be removed.
Then push all the remaining good needles back only as far as the sinker posts, so you can then bring the fauly needles to the hold position, you can now put the good needles all the way back to non working position and remove the sponge bar again and now replace the faulty needles.
The two most important parts of any Japanese machine are the needles and the sponge bar, considering the cost of a needle why would you not replace faulty ones.