top tension check for cotton stuck between tension discs that may cause problem.bottom tension check cotton or dirt on tension spring of bobbin case,after wiring when cotton is pulled with pressure foot down needle should move slightly before cotton start moving with tension at 4,lower tension checked with bobbin case hanging on thread and when small upward jerk is performed bobbincase should move approx 1cm down.hope explanation make sense
johan
October 2014
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