1999-2004 Honda TRX400EX FourTrax Service Manual, Page 68Get this manual
FUEL SYSTEM Check the jet needle for stepped wear or damageCheck the throttle valve for scoring, scratches or damage
ACCELERATOR PUMP
Remove the three screws while holding the accelerator pump cover
Remove the pump cover, spring and the diaphragm, being careful not to damage itVisually check the following: -diaphragm for deterioration or pin holes -spring for deterioration -diaphragm shaft for excessive wear or damage -orifice in cover for clogging or restriction