I am fairly new to sledding. I have a 97 Formula 500 liquid with 4000 miles. I replaced the rear shock as the original was worn out/pitted shaft. After putting in the new one (Kimpex Gold gas), I sat on the sled. The suspension dropped quite a bit and didn't spring back. When I got off, it came up a bit, but not much. The spring tensioners are adjusted to the heaviest setting. It will stay up once lifted. I checked the front, larger shock and it was fine. No broken springs and all shafts well greased, nothing seems to be problematic. I haven't had it out for a ride since (not much snow). Is this normal? Will the suspension be fine once the machine is moving? Do the springs get weak/need to be relaced?

Yes, the torsion springs do get tired and require replacement.

how tight are the bolts on the suspension?

when I put my suspension back on this fall I had tighten the bolts too tight

hence when sitting on the sled it would sag but when i got off it would not come up

I loosen the bolts abit at the pivot point and now she comes up :)

If you change out the springs get the ones for the mxz there stiffer.
Also look at the plastic keepers the spring ends fit into on the rail . IF there wore it will hang up and bind too . Make sure the spring ends are smooth and not rusted also . I always cleaned them up and added some grease on the part that slides in the keeper . If there rusted up they will eat the keepers till the rust is wore off.