check your oil, when was the last time you changed your needle? I find I need to change mine for every quilt, check for lint between your tenisen disk's. Is your new thread the same brand and weight? I have found that some brands the color seams to affect the way a machine will accept it- blks can be a ruffer feel than say cream or white or even dark brown. These problems happen to everyone and on every machine. once you learn how your machine likes to be treated it becomes second nature to keep her running smoothly. Good luck