Stitches straight for aprox 10 stitches and then wanders for 2 or three stitches: then straight again for 10, wanders for 2

If you haven't removed the top to clean and oil the cams then likely they are stuck, hence zigzag.

not sure if this will help you out..if you scroll to the bottom of this page on the left you will see Previous Lessons:
lesson 1: Welcome and intro first,
lesson 2: Guide to Buying a Sewing Machine
lesson 3: Sewing Machine Supplies
lesson 4: Getting to Know Your Machine
lesson 5: How to Thread Your Machine
lesson 6: How to Sew a Straight, curved, and corner line
lesson 7: How to Sew a Basic Seam
Lesson 8: Trouble Shooting Your Sewing Machine
Lesson 9: Basic Sewing Terms

Next Lessons:
Lesson 11: How to Read a Pattern Envelope....
Sewing Lesson 10 How to Fix Tension on Your Sewing Machine ..try this link.

set the machine to straight stitching which should keep the needle in the center position
a zipper foot is a normal foot with 1/2 missing
It it still wanders , take it in for a service

1. Put a piece of paper on the sewing machine w/o thread. Sew for three inches.
2. Notice the needle holes are straight with the feed dogs. The pressure foot is not in line with the holes.
3. With the pressure foot down loosen the pressure foot pressure to it's lowest amount.
4. There is a screw on the arm that needs to be loosened. Afterwards, adjust the arm until the foot is parallel with the feed dogs. Tighten screw.
5. Try sewing again on the piece of paper to check for accuracy on being straight.
6. One other check is to insure the feed dogs have even wear.

The "dial" in the back is for decorative stitches which require a "programmer" to be inserted with the stitch formation you want to form. For a straight stitch no cam is required in the back of the machine. The three dials on the front:

Upper Left: Stitch selector
Upper Right: Stitch lenght
Lower: Stitch width

Using the upper left dial select the straight stitch picture
Using the upper right, choose your stitch lenght
Using the lower, choose your needle position, left/center/right

If you can grab the hand wheel and move it right and left, then it probably needs a plastic collar that goes next to the left upper shaft bushing.
If not then the cam timing needs to be adjusted.

Your machine needs retiming, if you email me I will attach instructions, quite straight forward but remine me of your model [email protected]

Hello,
#1- tension settings, set this to "5" and leave it
#2- width control setting, 0 would be straight while 5 would be the full width of the stitch (would make a wide zig zag)
#3- Length control, larger the number, longer the stitch. (usually you will set this from 1.5 to 2.5)
#4- Stitch selector, match up the number with the stitch you want to sew. If you want to use the lower row of stitches (14-25) set the length dial to "ss". (ss stands for stretch stitch, such as for #14 (three rows of straight dashed lines) instead of just sewing one stitch forward, the machine will sew back and forth giving you a stretchy stitch/stronger)

Let me know if you need more help :) Chris

The selector finger that runs on the camstack may be between the straight stitch and the zig cam, you need a shop adjustment

timing issue, needs to be serviced and re timed.