JUKI MOL-254 Engineer's Manual page 213

Trouble
2. Needle breakage
3. Stitch skipping
Cause (1)
Clearance provided between the needle and
the needle guard section of the shuttle driver
is improper.
Clearance provided between the needle and
the inner hook is improper.
Feed timing is improper.
Needle comes in contact with the moving
knife.
Needle comes in contact with the presser.
Needle comes in contact with the wiper.
Needle is bent.
Needle is too thin.
There is a scratch in the needle hole guide.
Clearance provided between the needle and
the inner hook is large.
Needle-to-inner hook timing is improperly
adjusted.
Adjustment of the clearance provided
between the needle guard section of the
shuttle driver and the needle is improper.
The sewing product is apt to flop.
Needle is bent or has a blunt tip.
Needle thread loop falls.
Cloth feed timing is improper.
Loop end is not pressed.
4 mm
Cause (2) Checking order and adjusting procedure
Adjust the clearance provided between the needle and the shuttle
driver.
Adjust the clearance provided between the needle and the inner
hook.
Change the timing.
Adjust the position of the moving knife.
Adjust the position of the presser.
Adjust the installing position of the wiper.
Replace the needle.
Change the needle to one suitable for the sewing product.
Remove the scratch, or replace the needle hole guide.
Adjust the clearance provided between the needle and the inner
hook.
Adjust the needle-to-inner hook timing.
Adjust the clearance provided between the needle and the shuttle
driver.
Take up the slack in the sewing product.
Replace the needle.
Attach the needle with its long groove slanting slightly. (Approx. 20fl)
Change the timing.
Adjust the loop supply device.