1999-2004 Honda TRX400EX FourTrax Service Manual, Page 256Get this manual
TROUBLESHOOTING
POOR PERFORMANCE AT HIGH SPEED
Possible cause
1Disconnect fuel tube carburetor
Fuel flow restricted
Fuel flows freely
2Check carburetor for clogging
Not clogged
Restricted fuel tube Restricted fuel tank breather tube Faulty fuel valve Clogged fuel strainer
Clogged
bCarburetor not serviced frequently enough
.c 3Checkvalve timing
Correct
Incorrect
Cam sprockets not installed properly
4Check ignition timing
Correct