2005-2009 Honda TRX400EX/TRX400X Service Manual, Page 89Get this manual
FUEL SYSTEM AIR CUT-OFF VALVE Remove the fo ll owing- screwair cu t-off valve
slow air jet a-r ings
Apply vacuum to the vacuum port (hose)The vacuum should mainta ined ir should not flow hrough the valv ports when th vacuum is applied, and should low when the vacuum is not appl ied