JUKI MOL-254 Engineer's Manual page 218

Trouble
From the previous page
7. Poorly tensed stitches are made.
Cause (1)
Thread trimming solenoid fails to work.
(Far side)
Thread trimming cylinder fails to work.
(This side)
Cylinder solenoid valve (This side)
Adjustment of the thread tension No. 2 is
improper.
Thread tension No. 2 is rising.
Adjustment of the thread take-up spring is
improper.
Clearance provided between the inner hook
and the shuttle driver is improper.
Selection of the needle used is improper.
Selection of the needle hole guide is
improper.
Feed timing is improper.
Cause (2)
Replace the solenoid.
Tension of the thread take-up spring is low.
Stroke of the thread take-up spring is large.
Needle used is thin.
Hole diameter of the needle hole guide is
small as against the needle used and the
thread.
Checking order and adjusting procedure
Replace the solenoid.
Replace the cylinder.
Replace the solenoid valve.
Adjust the tension of the thread tension No. 2.
Adjust the thread release mechanism.
Adjust the thread take-up spring.
Adjust the stroke of the thread take-up spring.
Adjust the clearance provided between the inner hook and the shuttle
driver.
Replace the needle with a thicker one.
Change the needle hole guide to one with large diameter of the
hole.
Change the timing.