- even if that spot is the same thickness, if the fibers there got more squeezed, then there's more fiber in that spot than in other spots; more fibers to take up the same amount of twist may result in a less overall-twisted spot, as there is more fiber in that spot to resist the twist.
- that could be a spot that got some felting from being in your hand; I have had a terrible time in the past with partly felting during drafting due to my sweaty death-grip on my fiber. Now I hold my fiber like it is a baby bird, and my hand stays cool and dry from less stressful holding too. My lead, drafting hand does the gravity/drop-preventing holding so that my back hand need only hold softly and gently to prevent gumming up (or, felting up) the roving that has yet to be drafted.
I recently spent an afternoon re-drafting/spinning some old singles to match some new spinning I'd done for the plying stage, and found some thicker parts were more felted and very resistant to being unspun and re-drafted. But the third recommendation I can make is to hold your yarn with your hands at least 1.5 staple lengths apart, with a fat spot in the middle, and untwist it to redraft out the fat spot. Staple length is the length of the individual fibers -- if your hands are 1.5 staple lengths apart, then they can't both be holding onto the ends of a particular strand of fiber.
I do this untwisting and redrafting alot when my drafting is uneven (which means I get alot of practice at this ;-) ) so that I can wind on a more evenly spun yarn. You see, I'm one of those people for whom the adage "just ply your thick & thin yarn, the thin spots will meet up with the thick, really" just does not apply -- thin meets thin and thick meets thick, for me, 95% of the time. So the singles have to be spun evenly or I'm spinning unintentional art yarn.
I wouldn't just add more twist overall, as it will migrate to the thin spots and they'll get all kinky and coily. I'd try opening up and redrafting the thick spots out to have a more even single. Or, I'd try enjoying being able to spin art yarn :-)
Now, if I am trying to spin a thick-and-thin yarn like the one shown, then it's simply a characteristic of the thickness that the thick spots have less twist than the thin spots. You can try to force a bit more twist into thick spots, but usually it migrates to the thin areas all on its own. So you end up with variable twist in your yarn. With yarns like this, I will be sure to rough them up when washing them, to full the yarn a bit and ensure the more softly spun thick spots stick together.***
Related posts:
Posts on spinning singles
How do you make a good-looking 2-ply yarn?
What does it take to win a yarn competition?
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