Sewing machine

[dragontattooist.livejournal.com]

I need some help guys and Im really hoping someone can sort me out! I have a singer sewing machine, a pretty basic but durable one. Ive always had problems with the tension and right now, its driving me mad. It seems to be no matter what I do, the stitching is very loose or very bunched up and scraggly. Ive adjusted it, cleaned it, taken the whole casing to bits and cleaned it with a nice soft brush but nothing is helping.
Right now, Im getting loose stitching on the underside of the fabric. Im currently sewing my wedding dress so its really important I can sort it out. Ive looked all over the net and everywhere seems to say different things - that the cheaper singers are set up badly and need a professional to fix them; that you can fix the tention yourself on the bobbin but some sites say this is machine suicide...argh!!!!

For a normal cotton what should my upper tension be set to? I just took up a dress for my sister and ended up picking everything out; the top stitching was really tight and gathered all the material. Im wondering if the only way to fix it is to throw it out the window >_>;

Thanks in advance!