Hi, i was wondering if i buy Dna stage 2 Filter cover to my xt 660 X (model 2005) does the engine need fuel mod or something else modifications? The engine wont go too lean? Thanks a lot.

Well it is recommended that you do, however you can get away without using a fuel mod, but you need to increase the CO2 levels through the dash by doing what we call the fuelling fix, see this link: http://www.xt660.com/showthread.php?t=55&highlight=Co+adjustment