1999-2002 TRX400EX Fourtrax Service Manual, Page 74Get this manual
FUEL SYSTEM Install the throttle stop screw with the washer and spring by screwing it clockwiseSecure the stay with the screw by aligning its hole and bossTurn the throttle stop screw to align the butterfly throttle valve with the edge of the outside by-pass hole in the carburetorTHROTILE STOP SCREW
AIR CUT-OFFVALVE
Install new O-rings onto the air cut-off valve into the joint pipeInstall the joint pipe into the air cut-off valve with the stepped side facing out (valve side)