I believe Amos or someone may have made a post about making a Kraken more gamable. I don't have the link off hand but the first few things were; spring (downgrade to an M110 if playing outdoor, aim for 360-380 FPS), compression parts (piston, cylinder, piston head, cylinder head), hop up bucking (I think Prometheus Soft bucking is the recommended one), and inner barrel (doesn't have to be a tight barrel just make sure the inner diameter and "straightness" is consistent).
Also note that the spring is crap on the Kraken and they usually settle very fast so I'm told. You may start off shooting 410 FPS but it will gradually get weaker and maybe settle in at 380 or less. Nonetheless you should get a spring that's more consistent and doesn't "settle" like the stock Kraken spring. Something like a Modify S110 or S120 will be perfect. Keep in mind a little bit of settling is acceptable after a "breaking in" period however it should only be a few FPS difference.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE