Originally Posted by chris_quilts
This may not be it but have you cleaned out the bobbin area? Delinted, debugged and whatever else may be residing there. I had a similar situation and once all the old lint and mummified bugs were cleaned out and all was oiled, the machine sewed beautifully for me. Other than that, no other suggestions.
Actually there is one thing I forgot to say - there is a little red piece of gunky felt in there - next to the little button you press to make the bobbin jump out. I tired getting it out and decided it bellonged there - what do you think? - everything else is cleaned up and oiled??