@mkc and
@cashs_mom - so interesting about the properties of linen! I will definitely try now with another fabric and report back.
I also realised that the tension is wrong on the darker stitches in the example photo. I will try again with it set better and also follow your suggestion of tighttening the tension
@quiltedsunshine - good plan.
More testing to do, and a service I think - and I'll keep my eyes peeled for a Juki TL 2010 in the meantime.
Thanks so much everyone, I really appreciate the suggestions.