Sorry about the timing, it is such a PAIN. But it sounds like it might not have been totally timed correctly when you got it back. I have a Pfaff and I had to take it in when I blew my timing too, the man that worked on it just didn't get it spot on. I would sew for a few days maybe even a week and then my timing would be out again. Fixing a sewing machine is like fixing a car, the manufacturer has guide lines for setting the timing it should be between "X and Z". Each machine (even the same models), are different they might have 6 in a row that can take the timing at "Y" but then you get the machine that wants the timing at "X and a half". This is why it's hard to change or get a new sewing machine doctor, our machines are like us each one is the same but different.