if the puckering is on the bottom of your paper piecing it would have something to do with the top tension- not the bobbin- perhaps when you were cleaning/servicing you tightened the top tension a little? or perhaps the thread is not correctly in between the tension disks- (try/practice/trouble shoot with fabric and paper instead of just fabric- did you change the paper you had been using? a heavier paper could effect the tension setting- try loosening the top tension just a little at a time & see if that helps-