Varying stitch length with Cobra 4

[CliffFendley]

I am getting varying stitch lengths with my Cobra 4. When I first start a stitch the stitches will be longer and then get closer as I sew along. Also as the stitches have gotten shorter when I reverse to back stitch the stitches are long again and don't follow the stitches on the backstitch.

I was first thinking it was the leather and was getting some slipping and not feeding but sewing slow I can't notice any slipping it's almost like it's actually changing the stitch length as I sew. Can someone tell me what to look for? 

Thanks for any help.

[Kcstott]

Are you using the lock on the stitch length lever? And is it locked? 
have you messed with the wedge above the lever on the slot? 
that wedge is used to calibrate forward and reverse and if mucked with will screw up the matches stitch length. 
as for the machine changing stitch lengths  I have no clue there. 
come Monday id give leather machine co a call and see what they offer. 

[Hildebrand]

Look for a spot in the thread path where the thread is getting caught. Each time I have had stitch length issues it was because the thread was catching somewhere, usually on the back side around the pressor foot lift mechanism. 
Todd

[CliffFendley]

Thanks I'll look things over good again but it's been a gradual more occasional thing especially with thick pieces but recently it's gotten bad and consistent. Might have to give them a call.

[CowboyBob]

There can be a few reasons for this & one simple one is a loose feed dog screw.