Help, Quilting fighting back

[Ploshkin]

I spent a fair part of yesterday, on and off, FMQing and whizzing up and down a ruler without any problems (apart from my lack of skill).  By the time I got to do a sample block things were going quite swimmingly so today I went and got some thread to do the actual quilt.
I got YLI cotton quilting thread (40 weight) which I have used for most of the quilting things I have previously done including a bit of FMQ.

The machine was still set up exactly as yesterday (ruler foot on, feed dogs down, stitch length 0) so I threaded up with my new thread and stitched a bit on a sample.  To start it was skipping a lot of stitches then when I was going sideways it wasn't picking up the bobbin thread at all.
In brief, I have rethreaded my machine numerous times, used a different bobbin, taken half the thread off a bobbin in case it was too full, and used the top thread reel vertically and horizontally, tried with the feed dogs up, tried with the feed dogs down, but am getting no stitches forming.  I can bring the bobbin thread to the top ok but thereafter it just won't pick up the bottom thread at all or at best about one in 10.

I went back to the thread and bobbin that I used yesterday - same weight thread (40) but polyester, not cotton.  It stitched perfectly.  Went back to the cotton thread - nothing.  I tried other cotton threads that I had previously used with no problem - nothing.  I took off the ruler foot and put on the 1/4" foot - perfect stitching!

As it was stitching ok with a standard straight stitch I thought I would at least do the stitching in the ditch along the sashing strips.  After 6 rows of stitching I noticed a couple of loops on the top of one of the rows.  I looked at the back and the last 3 of the 6 rows had a tight bottom thread and a loopy top thread.  I checked the threading and nothing had jumped out.  The bobbin was nearly empty so I changed the bobbin and it is stitching perfectly again.

I just can't fathom why it will stitch fine with a normal foot but won't with the ruler foot (but will with the polyester thread).  My machine (Pfaff Ambition) has never, ever been picky about thread.  Of course it might just do something completely different tomorrow.

Any clues anybody?  I'm tearing my hair out here!

[Kad]

Can I suggest that it might help if, when using the YLI cotton quilting thread, you use a slightly larger needle size.
Yes, I know that it's the same weight as other threads that are behaving beautifully but I almost always use YLI quilting thread and often get the same problems as you're having if I forget to change the needle for a slightly larger one.
 I also use a 'non- quilting' thread in the bobbin, just one that blends in with the backing fabric.
Please don't give up on the quilting rulers, they get to be quite addictive, is so I've found 

[Ploshkin]

@Kad what size needle do you use?
I was using a size 75 quilting needle and I did try a larger one but didn't have anything bigger than a size 80 (it wasn't a quilting needle).
I hadn't thought to try a different thread in the bobbin, I'll have a go at that.

[Kad]

I usually piece with a size 75 or 80 , so would use a #90/14 for the quilting stage.
I always use 'non-quilting' thread in the bobbin - better choice of colours and  cheaper

Good luck.

[Iminei]

                                

When things go wrong more than three times it is time to

Step away from the machine and toward the beverage of your choice.

[Ploshkin]

Thank you @Kad I'll order some size 90 needles and I'll also have another bash with a different bobbin thread.  I've still got a fair bit of straight stitching to do round the sashing then I'll tackle it again.

[rubywishes]

Yes, perhaps a 90/14 needle would be the go?

[Deafoldbat]

I would use a 90/14 needle for quilting.

Is the YLI thread the 'old' smooth and shiny stuff or the new 'fuzzy' one. I had similar problems a couple of years ago - until then I'd always used YLI - when I started a new spool and had skipped stitches. The new thread spool wasn't as smooth and glossy as the older ones I had; apparently production has been moved to Mexico and the thread isn't exactly the same. Since then I've used King Tut or Aurifil 40wt cotton and had no problems.

[Ploshkin]

That's interesting @Greybird it's a reel I've just bought.  I did though try some King Tut thread that I had used previously but still had the same problem. I have some 90 needles on the way.

[Greybird]

? would like to have been able to help @Ploshkin but I'm afraid all this is beyond me. I think it might have been @Deafoldbat you meant!

[Ploshkin]

  sorry, @Greybird too early in the morning for my brain.

[Ploshkin]

Well, after countless combinations of thread plus a size 90 needle and a straight stitch plate I found that nothing would work consistently with the cotton thread even if I used non cotton in the bobbin (straight stitch fine, free motion not).  It seems to work ok, just with an occasional skipped stitch, with polyester thread so I'm going with that.