Relative

Hopefully that should show needle to hook timing. Sometimes the thread goes on the wrong side of the part circled as shown in the image below. When this happens it makes a "plunk"/click sound because the thread gets tightened and slips off. Is this something to do with the hook thread opener opening too soon?:

What's with all the needle positioner hate aha But I think you guys may be on to something. I did a little testing this afternoon and found that if I set the needle position to the up position then this problem doesn't happen. Yet if I leave everything the same and only change it back to the down position, the problem begins again. Any idea of why this is? For the longest I thought it some kind of bobbin backlash. However on the cylinder arm I slid the bed plate so I could watch the bobbin and see what was happening. When I stopped sewing I put a finger on the bobbin and used the tip of a pen to press against the thread to check for any slack. Now I don't know what the correct amount of slack or lack there of there should be but to my un trained eye there was none. In the past I used a size 18 but always had trouble getting "good" tension. I could never get the knot to sit in the middle, I'd tighten the top tension and eventually the knot would shoot out the top of the fabric with a lot of force. Hence why I switched to a 21 as I find it easier to get a better stitch. I always but it down to the Cordura as I've sewn vinyls before and used a 18 needle without any issues. Another thing I thought, is it possible that I'm using too heavy duty machines for what I'm actually sewing? For example I noticed that when I layer up to 4 + I can typically get a good tension and not have the bobbin issue occur. I suspect it is still being pulled up but because the stack of fabric is thicker its simply hidden inside. On the 1541 I'm mainly topstitching zippers so 2 layers cordura, 1 zipper, 1 lining and on the 1341 its 3 layers of Cordura and 4ish lining. I just find it very strange that this happens across multiple machines yet I'm the only one to run into this. I have noticed another potential issue on the 1341 clone where the top thread sometimes gets caught on the wrong side of the hook after going through the hook thread opener and makes a kinda "plunk" sound as the needle goes back up. Will add pics tomorrow. Thanks guys

Hello all, I have had this issue for a long time. I can sew normally fine however when I stop mid stitch is when the problem happens. I take my foot of the pedal and the needle gets buried due to the needle positioner. I do not touch the work or make any changes, no lifting the presser foot, nothing. I then begin sewing again and for the few 1 - 5 stitch the bobbin thread gets pulled to the top as shown in the images below. To my knowledge I have tried everything. Increase / decrease bobbin tension Increase / decrease top tension Increase / decrease check spring stroke Increase / decrease check spring pressure Increase / decrease needle sizes Increase / decrease presser foot pressure Changed thread, lubed/non lubed, bonded/non bonded, nylon/polyester, thread brands Increase / decrease tension on bobbin winder Checked thread path Checked for inconsistency on how the thread comes off the spool Currently using 135x17 21 with Tex 70 I mainly sew 1000D DWR + PU Coated Cordura. This problem also occurs when I sew webbing. This machine occurs on multiple of my machines which leads me to believe its a ME problem but I don't know what I'm doing wrong! Its happens on an old Juki 1541 and a new 1341 clone. I notice it more on the 1541 as this is where I do all my top stitching, my solution has been to back off tension, thus making my overall tension not very good but its the only thing that helps. I had this problem when I bought my 1341 clone, the sewing tech looked it over and couldn't find any problem with it. The only alternation he made was to increase the bobbin tension substantially. I always used the drop test method but I'd say the bobbin tension more than doubled which of course made it harder to get good tension. I have asked around from people in the manufacturing industry, the little I've asked, have no idea what this could be.You may ask how I know that its when I begin sewing again. I know this because when I stop with the needle buried, without lifting the presser foot, I make a mark on the fabric next to the foot. I'm at my wits end. As I the operator is the common denominator I will describe my steps: Wind a bobbin is needed. Thread it through the bobbin tension, then the bobbin then wind it. Place it in the bobbin case as shown in the manual. Thread the machine as shown in the manual. Pull bobbin thread to the top my holding needle thread. Place work under presser foot. Bury needle Hold on to thread tails and begin sewing. Take foot off pedal to stop sewing. Put foot on pedal to start sewing and this is when the error happens. I thought I'd ask here before ringing another technician to come and have a look at it. Thank you