LDD
As you might have imagined I have tied hundreds of lipped flies and have had a difficult time narrowing down what actually causes a particular pattern to spin. I believe some patterns incorporating a FlyLipp spin no matter what I do, so obviously the Lipp is a factor. I have tied other patterns that "occasionally" spin, some I am able to correct, others not. And then I have tied patterns that never spin. Unlike large lure manufacturing companies, I don't have access to the testing facilities or to stringent control of manufacturing tolerences. Hand tied flies are just that, and even subtle variations make a difference, therefore isolating the exact cause of spin is difficult, to say the least. But I am narrowing it down so it is not the problem that it used to be. Balance seems to be the biggest culprit. I have read where "some flies spin when they are out of balance", I have found just the opposite to be true. I think flies are more apt to spin if the are perfectly balanced, much like a pinwheel. By offsetting the weight or the resistance of mass, a fly is less likely to spin.
However, to answer your question, yes I do use a #8 swivel. Originally it was to compensate for spinning. However, I continued to use them even though they are no longer necessary. They actually makes a lot of sense. They make changing out tippets much easier, like going from mono to wire, or heavy to light, or simply putting on a new tippet. It only means tying a single knot. Secondly they make a leader last a LOT longer, you don't "eat" into your leader section every time you change tippets. I make my own furled leaders and incorporate the swivel right into leader construction. I could fish an entire season and never have to change leaders, only tippets. And thirdly, I actually vary the size of swivel to increase or decrease the sink rate of my leader section. I usually fish a floating line in six feet of water or less. However, I construct most of my leaders from flourocarbon to increase their sink rate. This allows me to fish a floating line with a sink tip. But some flies I have designed actually float. A larger swivel will act as an anchor and the fly will suspend above it, but only the length of the tippet material. The first stripping motion causes the FlyLipp to dig in and the fly darts to the bottom. And a long strip will even kick up a nice mud plume.
Sorry to get so carried away, I just love this stuff!
Greg