Lionel Smoke Unit - Repack - Use all the smoke rope?

I usually use it all.  If a little too much, put some fluid on it to help it settle down while doing the final touches...

Not all smoke units are created equal. The plastic smoke bowls in later Legacy models seem to me to be a fair bit smaller than older metal units and going back further some track-powered smoke units are pretty large. Then there are differences between locations of the air inlets from the fan to the bowl, which must not be blocked the wicking. The rope wicking is more than enough to fill any of these. I generally start with half of the rope and add more if needed, bearing in mind where the inlet is. 

I keep stuffing it in until no more will fit.  As Hancock52 states, wet it down with smoke fluid to keep it in place, it's kinda' like hair gel for smoke units.