It is all steel(metal no plastic) industrial (came in a necchi table). When I used 100% nylon thread no problems till needle broke; replaced that and tried to sew with same brand of thread but it was 100% polyester, the polyester thread kept coming apart and bunching up at the needle. We never adjusted anything; except replace the needle, so how do we troubleshoot this and where do we find a manual for this model (seems to be a unique one as I can't find it)???

Sewing Machines - Necchi