From: Calgary Area of Alberta
My aunt used to borrow my grandmothers portable singer... every single time she returned it this would be the state of affairs... thread nests... my grandmother was a saint I would never have let her borrow it in the first place....
So one day it is sewing just fine and then next time you use it thread nests??? so what has changed??? once you have thoroughly cleaned it - I have a tiny woodworking brush it looks like a mascara brush that can really help - Lee Valley online has a catalogue if there is no such shop near your location. Obviously you cant use mascara brush unless it has been thoroughly cleaned... don't use air dust buster thing like for electronics it will push lint further into the bowels of the machine. Might be the thread... not sure how you would adjust tension to go from a very fine thread to upholstery type thread... have you sewn fake fur type hairy fabric or fleece... if you have more than one machine do you have the correct bobbin... I only have Janome machines so no chance of using the singer bobbin in the Janome... all else fails haul it into the shop for service... sometimes the tune up price is worth your sanity... time = money...
Shirley - Mom to Dickens (PuppyWuppy now known as Dicky Wicky)and Doyle (baby) and Baxter, Bella, Pistol, Cowboy, ChiChi at Rainbow Bridge
I sew on Janome 8000, 10001, 11000se, 12000, 350e, 300e, Janome 234d and Babylock Imagine