JUKI MF-7900 Series Engineer's Manual page 35

Adjustment procedures
1. To adjust the timing relation between the needle and the looper,
remove the top cover, loosen four setscrews ❶ in the sprocket
and turn upper pulley ❷ in the state that the sprocket is held.
2. Adjusting procedure
(1) In case dimension A when the looper advances (going) is
smaller than dimension B when the looper retreats (returning),
the looper timing is retarded (needle timing is advanced). In
this case, loosen setscrews ❶ in the sprocket and finely turn
upper pulley ❷ in the reverse direction.
(2) In case dimension A when the looper advances (going) is larg-
er than dimension B when the looper retreats (returning), the
looper timing is advanced (needle timing is retarded). In this
case, loosen setscrews ❶ in the sprocket and finely turn upper
pulley ❷ in the normal direction.
(Caution) Be careful not to excessively turn upper pulley ❷ .
After the adjustment, fix four setscrews ❶ in the sprocket.
3.
Results of Improper adjustment
◦ When the difference in timing
(going and returning) of looper is
excessively large, stitch skipping
or entangling of needle thread
will be caused.
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