Can't get the tension or the stitches to regulate

The tension has nothing to do with the feed dogs. All the feed dogs is move to pull the fabric through the machine. Tension regulates the amount of tension applied to the thread as it stitches.

Find the tensions on your machine. Usually a screw below on the bobbin regulates the top stitches tension. Usually a numbered wheel on top--where the thread is around it--regulates the bottom stitches. YOU NEED TO ADJUST THE TOP WHEEL, test on scrap material, and if looser, you are in the right direction. If it is still a mess. turn the knob to a lower number.

Please check the stitch regulator and check the bobbin tension and winding or you check the thread put properly. Otherwise you go to mechanic shop.

it's possible that it could be a thread tension or timing problem, when was the last the machine was serviced

The stitch length dial needs to be set to a lower number (number of stitches per inch) to give you longer stitches. The tensions do not regulate the stitch length, the feed dogs regulate the distance the material is advanced between stitches. Also, make sure the pressure foot is applying enough pressure to keep the material in firm enough contact with the feed dogs.
<Ray>

I had a similar problem with the long stitches. One of the encoders for the stitch regulator was not turning all the time when I moved the machine. My dealer gave me a new one and now the machine works fine. It could also be your cable from the encoders to the machine. If the wires (very fragile) get broken, either the machine won't sew when you go side to side or back and forth, or it will make the intermittently long stitches you mentioned.

It's important to have the foot raised when you thread the machine. If you have it down, the thread won't get caught between the tension disks, and it will be very hard to get consistent stitches.

There is a tiny screw on the side of the bobbin case.

Mark the **** (in the screw head) position on the bobbin case with tiny dab of nail polish so you will know where the original setting was.

Left/loose and right/tight.

If you are adjusting because the bottom stitching is loose/loopy, first try threading the machine with the presser foot up to see if this solves the problem.

Well is your machine skipping stitches? "Not looping" does that mean not creating a stitch? To adjust your bottom stitch you usually adjust the top tension regulator. I can try to help you more in detail check out my forums http://www.sewingmachineryrepair.com/forums/index.php

Probably the most important contol on your machine is this one that regulates your top thread tension there are reason for having to reset your tension.Classified your fabric that you are using there are several set up of tension in every fabric that you use.Cotton fabric is most easier other than silk fabric make a record on this set up.The required tension depend upon the stiffness of the fabric,thickness,layer of rabric to be sewn and required stitches.Try cotton fadric turn tension dial to N0. 3 and Stitch set to from 8 to 12 defend to what is nice to you.

You don't want to adjust the bobbin tension, you'll want to try adjusting your stitch length, as well as the regulator tension.