its a combo of spring tension and the friction the saucer the spring pushes down on and what it rubs across
some wax the bottom of the saucer, I've used powdered graphite
as for the spring, seen some tie wrap a couple of spirals together though this has never worked for me. My last stick was the worst about this. I take a 1/2 inch "C" pipe clamp and slip it under the back of the saucer when I'm not playing AH. It keep the spring compressed and breaks it in quicker. It also double as a great "auto pilot" for gv when in drivers seat and don't want to hold handle forawrd to go
If it's really bad, you may want to exchange it for another X45. Heard of some ppl opening the sticks in the store to get one that felt the best
here's a dat file if ur interested:
http://www.pogbird.com/X45/