Backside Stitch Almost Perfect

[ArchiveGoods]

Hello!

I have purchased a brand new Pfaff 335. I am so close to having the tension perfect, but after several test runs, I come up with the same problem. 

See the photos attached: I have circled the areas in question. I have tested different thicknesses of leather etc. and I still wind up with a single loose loop on the backside of the stitch every so often. How do I fix this? 

Additional Info: Needle: 134-35 #19, Amman Thread T70 (I am ordering #16 and #18 needles to test)

Thanks!

[Wizcrafts]

It could be a thread problem. If you have, or can buy more thread, try a different spool. Also, inspect the tension spring on the bobbin case to see if there is any thread fluff stuck under it, or inside the bobbin case. Make sure the timing is spot-on and not retarded. Try adjusting the travel and slack settings of your check spring.

[ArchiveGoods]

@Wizcrafts 

Ok, I will try another spool today. Are you referring to hook timing? 

I had a hunch about the check spring but didn't that could be adjusted. It feels tight and is not as fluid as my Consew 205RB-5.

Thank you!

[Wizcrafts]

1 hour ago, ArchiveGoods said:

Are you referring to hook timing?

Yes. Make sure it isn't either retarded or advanced to start your troubleshooting.

[RockyAussie]

This could also be just a badly wound bobbin. If your thread path from the spool is not a smooth run then the intermittent tightness can make the bobbin wind on with tight spots on and off. When the tight part holds up the thread as it feeds off of the bobbin it will pull the thread down as you have shown. It can also be if you have left any tail thread hanging out of the bobbin. Test with the bobbin in the machine a slowly pull out the thread and feel for any catching as it goes.

[ArchiveGoods]

@RockyAussie

That is something else I'll be looking into as well. My bobbin winds up smoothly and evenly, but I will watch more closely and double check. 

Thank you!!