Troubleshooting - difficulty adjusting take-up (tension)

By slowing down the flyer (Irish tension) or the bobbin (Scotch tension) you can better control the tension on the spun yarn.

With Irish tension spinning wheels, the twist is caused by the spinning of the bobbin. Because the yarn connects the flyer to the bobbin, it will also rotate. This results in tension on the yarn, caused by the force required to turn the flyer. By turning the leather brake strap tighter on the flyer orifice, by tightening the  knurled nut, you increase the pull or tension. If you need less  pull, you can also loosen the knurled nut and let the brake strap hang loose. A drop of oil on the orifice and brass bearing can reduce the tension even further.
With Scotch tension spinning wheels the twist is caused by the turning of the flyer connected to the pulley. 

Because the yarn connects the bobbin to the flyer, it will also spin. This results in tension on the yarn, caused by the force required to turn the bobbin. By turning the brake tension cord tighter on the bobbin, using the knob, you get more pull or tension.

For both systems, as the bobbin gets fuller, you'll have to slow your treadling down more, to maintain the same pull on the yarn. This means that the spinning wheel will pull a little harder as the bobbin becomes fuller.