JUKI MOL-254 Engineer's Manual page 212

Trouble
From the previous page
Length of the remaining bobbin thread is
insufficient.
The sewing product is apt to flop.
Threading the needle bar thread guide is
wrong.
Bobbin runs idle and bobbin thread
protrudes.
Setting of thread trimming angle on the
operation panel is wrong.
Cause (1)
Difference in height between the needle hole
guide and the counter knife is high.
Clearance provided between the needle hole
guide and the counter knife is small.
There is a scratch on the bottom face of the
needle hole guide.
There is a scratch at the thread spreading
section of the moving knife.
There is a scratch in the shuttle hook upper
spring.
Bobbin thread tension is too high.
Cause (2) Checking order and adjusting procedure
Adjust the height of the counter knife.
Adjust the position of the counter knife.
Polish the needle hole guide or replace it.
Polish with buff the thread spreading section of the moving knife, or
replace the moving knife.
Remove the scratch or replace the spring.
Adjust the bobbin thread tension.
Take up the slack in the sewing product.
Refer to the item "Threading the needle bar thread guide".
Use the exclusive bobbin and bobbin case for MOL-254.
Increase the tension of the idle prevention spring.
Adjust the setting.