Usually I Set the spring tension as high as i can get it. when its loose it causes friction and pedal board "jump", this makes it very hard to get going fast. Fredrik uses a Yamaha flying dragon driect drive pedal. Direct drive pedals have alot better action than a belt or chains.They are also alot "lighter" in a way, but it still takes alot of work. Derek Roddy the drummer of hate eternal uses axis pedals (another direct drive pedal) and can get his double bass up to 300 bpm.
The Best thing you can do is start slow and work your way faster Gradually. if you dont start slow and work your way up more than likly all of your double bass will sound like shit..
Hope this helps you.