JUKI LU-1510N-7 Engineer's Manual page 73

Troubles
Loose stitches
3
(Balloon stitches or
isolated idling loop)
Loose stitches
(Needle thread rises.)
* Use separately available parts below : "21144308 Needle thread lubricator"
Causes
Clearance between the
inner hook guide and the
protruding section of
inner hook is too large.
Thread paths have been
poorly finished.
Bobbin fails to move
smoothly.
Thread is not well tightened
in the reverse feed.
Height of the feed dog is
too high.
Feed timing is excessively
advanced.
Hard-to-slip thread is
used.
Needle thread has not
been fully pulled up.
"B1114012000 Thread guide rod"
"B91351230B0 Silicon oiler"
Checking
Check the clearance.
Check the finish of the
respective thread paths.
Check the change of
bobbin thread tension.
Walking foot is not of
top-divided type.
Compare the height
with the standard
value.
– 69 –
Corrective measures
Refer to "(6) Adjusting the inner
hook guide".
Finish using a fine emery paper
or buff.
Replace the bobbin or the hook.
Use the optional walking foot
and presser foot.
Refer to "(4) Height of the feed
dog".
Lower the height by 0.2 mm than
the standard value.
Retard the feed timing.
Use silicon oil. (Refer to * below.)
Increase the needle thread
tension.
Use the optional walking foot.
(Top-divided type)