How to fix Bittorrent periodic slowdown, download speed dropping

Sometimes Bittorrent downloads will regularly slow down, causing the download speed to look like a sinusoidal up and down slowing and speeding up as below (bottom graph):

This periodic slowing down and speeding up is caused by setting the upload speed limit too low.

For example, if your upload speed is 3,000 KB/s and upload is limited to 40 KB/s, you will see this behavior.  Try increasing the upload limit in your Bittorrent client such as Deluge, Transmission or uTorrent such that it is at least 1/20th of your download speed (3,000/20 = 150, so the upload limit should be at least 150 KB/s).

Hope this helps!  If so, leave a thank you comment!