I have an old Gritzner sole stitcher, the type that all the moving parts can be seen. It seems the thread snags in the shuttle hook. Sometimes it won't do this when testing on Vibram. Could the needle groove be worn and it's not catching the thread? or perhaps the shuttle hook needs refaced? Or some other problem. Any advice is helpful. I mosly use Barbours linen cord. The manual says 'left' hand twist (which I have) but have never known a lock stitch machine to use left hand twist, only chain stitch machines.
Thanks,
JesseLee