craftgrrl | singer inspiration troubleshooting

Hi-

I have a Singer Inspiration 4220/4228 sewing machine. I'm having a lot of trouble figuring out the stitch and tension settings appropriate to different fabrics. Does anyone know of an online guide or tutorial that will teach me how to set the machine for different fabrics?

The projects I'm working on now involve sewing denim, and sewing polyester. For my denim project, I want to use a straight stitch, but no matter how I adjust the tension or stitch length my stitches come out very small and tight, so much so that I can't use a seam ripper to undo them. I haven't started on the polyester piece as it's vintage and I don't want to do anything I can't undo.

If anyone can help me figure out the appropriate settings for these,or point me towards a user guide for this machine that might be a bit more helpful than the manual it came with, I would GREATLY appreciate it.

Thank you :)