Consew 255RB3 reverse lever bobbing?

[sandmanred]

I just picked up a the machine from a Craigslist ad.  It supposedly had just been serviced with a new needle bar, hook and tension assembly.  It wouldn't make a stitch when I got there but it helped me make a better deal.  I've resolved most of issues that I detected and have it stitching again but there is something not right with the reverse lever.  Anytime it makes a stitch anywhere between 7 and 10 mm it bobs down and back up right as the needle approaches top of stroke.  I'm getting reasonable close to the correct stitch however it is a bit short.  

It did not go beyond 7 mm when I got it.  I have it going past that now but I must have missed something in the procedure to have the reverse lever bobbing like it does.  Any insight on what to check is welcome.

Thanks!

[sandmanred]

It kind of looks like the it's a spring issue.  It's been a while since the machine was used or oiled.  With a little oiling the problem got better, it only bobs occasionally above a stitch length of 9 mm and even then it's sporadic.  I can easily hold the lever up and it stitches fine and doesn't make any awful noises.  

[Gregg From Keystone Sewing]

Most common is the feeder or feed dog carrier is bumping or hitting something.  Also less likely is the linkage is cocked off to one side and is binding.