Almost any Carburetor is about 2 '12 Turns out "Sometimes 3". Or another way to do it is to Start the Quad "Warm it up" let it idle as you turn the Screw just till the engine almost dies "Or dies" and then do half a turn back out restart it if it stalled and you should be good. Also for an Online PDF this one is good for your year also. I'll leae a Link below.
http://hondampe.com.au/docs/owning_a_honda/owners_manuals/motorcycles/TRX400EX-SPORTRAX-2008.pdf
http://hondampe.com.au/docs/owning_a_honda/owners_manuals/motorcycles/TRX400EX-SPORTRAX-2008.pdf