1999-2002 TRX400EX Fourtrax Service Manual, Page 257Get this manual
TROUBLESHOOTING
POOR PERFORMANCE AT HIGH SPEED
Possible cause 1Disconnect fuel tube atFuel flow restricted carburetor Fuel flows freely Restricted fuel tube Restricted fuel tank breathertube Faulty fuel valve Clogged fuel strainer
2Check carburetor for clogging- Clogged
Carburetor not serviced frequently enough
Not clogged
3Checkvalvetiming- ncorrect Correct
Cam sprockets not installed properly
4Check ignition timingIncorrect- Correct