You tune your LSN using two methods that I know of. I use the first one I'm about to tell you, but some people don't like it.

The first method is to get your engine up to running temperature (make sure you've set your HSN well before messing with the LSN too), pinch the fuel line going from the tank to the carburetor. The engine should idle for a few seconds (2-4 seconds), rev up, and then settle down and die.

The second method, which I believe isn't quite as accurate, is to get your engine up to running temperature, then let it idle for about 10-15 seconds, then immediately punch the throttle. If your engine gurgles like it is running too rich then either stalls or takes a while to get going, then your LSN is too lean. If you do the same thing, and right after you punch it then engine shuts off without gurgling at all, then your LSN is too lean.

Hope that helps.