Juki LK-1900A thread pulls out of needle

[Corvus]

I just picked up a Juki LK-1900A-HS Bar tacker and it makes beautiful bar tacks. Unfortunately it pulls the thread through the needle at the start of almost every tack unless there is significant tail. This is particularly frustrating trying to do multiple tacks in a row. I've dowloaded the engineers manual and checked adjustments. All look good. Thread is b-69 Tex 70 bonded nylon.

Any words of wisdom out there on what I should look at, adjust or otherwise tinker with?
Thanks!

[WhiskeyTwoFour]

http://www.juki.co.jp/industrial_j/download_j/manual_j/lk1900an/menu/pdf/instruction_eg.pdf

Have you gone through page 54?

[Corvus]

http://www.juki.co.jp/industrial_j/download_j/manual_j/lk1900an/menu/pdf/instruction_eg.pdf

Have you gone through page 54?

Thanks, I focused back in on that section and I think I have it worked out.

[WhiskeyTwoFour]

Good.  If it persists, email Juki support.

[Gear Dynamics]

http://www.juki.co.jp/industrial_j/download_j/manual_j/lk1900an/menu/pdf/instruction_eg.pdf

Have you gone through page 54?

Thanks, I focused back in on that section and I think I have it worked out.

What was your solution?

[sodjer]

Hi Corvus ,I had the same problem ,with the same machine .only difference mine was intermittent.
I could run it all day without problem ,next day I had to rethread after 5 tacks,next day good again .
I looked at my threading ,I changed needles ,even room temp ( it seemed to happen when it was cold in the workshop )
I changed the company who supplied my thread and I haven’t had any more trouble .

[Corvus]

Following up on a couple questions...

I spent about a day adjusting the thread take up spring and 2nd thread clamp (disks next to the take up spring), which also means you have to adjust the 1st thread tension. It was trial and error as I don't have a spring force measurement tool. This seems to have worked, and if I start to get intermittent problems again I'll switch thread a different brand. I'm almost through this spool, so hopefully changing thread won't mess up what I've done, but I have a clearer picture now of how to make these adjustments. The room temperature thought is an interesting one I'll pay attention to also.

[Gear Dynamics]

Also what kind of thread are you running?

[Corvus]

Thread - 69 nylon bonded, I did switch spools soon after my last post and this spool is functioning well.

After I got it dialed in, I also adjusted the cutting knife moving blade and checked the other blade for spec. I need to play with this some more as I occasionally get a tack that doesn't cut the needle thread. I didn't check the knife edge, so it could well be a dull knife for this issue.

Neat machine to start learning about, thanks for all the support!

[SunriseTacticalGear]

I have the same machine and am running A&E T-70 through a #21 needle, between 800-1200 SPM?
Along with thread tension as stated above, I had great results by replacing my hook with a new Juki branded one. It costs a few dollars but my stitch was noticeably better.
I also give the machine a good cleaning in the hook area as well as cleaning the gunk out from under the bobbin case spring when I notice problems.
Scott