I have the older sibling of the Dart, the Judy. Mine is very stiff too. the preload on mine works though. on the firmest setting it barely moves 2mm when i hit a huge bump. on the lightest setting its softer but i still have to hit a good size bump to get it to activate. the wierd thing is i weigh 200lbs. if the stock spring is for 160 to 180 it should activate much easier than that. i ordered the soft spring (140 to 160lbs) and a tuning kit (in case the soft spring is too soft, which is highly likely for me hehe) i figured it was either mess with the springs or save up for a new fork.

btw i thought mine was fine until i tried my wife's Reba. damn the better bikes!!