Singer 16-141 stitch length varies

[Kaw550]

I have a singer 16-141 that be belonged to my grandmother.  

To get started, I am working with vinyl on a small project.

I have run into a problem with the machine.  I am trying to sew a fairly large stitch using 135 or 96 thread.

If I go really slow, one stitch at a time it is fine. When I get up to half speed the stitches start getting smaller.   With a clutch motor it's tough to maintain the low RPM's.

Any ideas?

I have played with the tension adjustment and the knob on top that adjust the foot pressure. 

 

[Constabulary]

maybe feed dog teeth worn or feed dog set too low

[Matt S]

How are you feeding the needle thread? If it's from a reel on the pin on top of the machine (like a domestic machine) it can get hung up easily, especially at higher speed. Much better to feed from an industrial thread stand, going through the hole in the pin on top of the machine. Restriction of the needle thread can reduce stitch length.

If you have a clutch motor you can slow the machine using your right hand on the wheel like a brake. If you drive a manual transmission car its a bit like controlling the car with brake and clutch only.

[Kaw550]

I had adjusted.the machine, including the feed dogs based on a manual I found online.  I used a razor blade as a straight edge to make sure the height was correct.  I am concerned they are a little worn.  There is definitely a difference compared to the new walking foot.

 

Last night I reinstalled the thread stand and backed the tension way off on the bobbin case and tensioner.

 

Things seems to have improved.

How can I confirm the correct needle length for the machine?