1999-2002 TRX400EX Fourtrax Service Manual, Page 77Get this manual
FUEL SYSTEM
HIGH ALTITUDE ADJUSTMENT
Below 5,000 ft (1,500 m) Mainjet Pilot screw opening #148 Factory preset Between 3,0008,000 ft (1,0002,500 ml #142 turns in from factory preset
The carburetor must be adjusted for high altitude riding (between 3,0008,000 ftl ,OOO2,500 mJSTANDARD SETTING: Below 5,000 ft 11,5OJm) HIGH ALTITUDE SETTING: Between 3,0008,000 ft (1.0002,500 ml The high altitude carburetor adjustment is performed as follows: Removethe carburetor (page 5-3) and the float chambercapReplace the standard main jet with the high altitude typeHIGH ALTITUDE MAINJET #142 Check that the O-ring on the chamber cap is in good condition and replace it with new one if necessaryInstall the chamber cap and the carburetorTurn-in the pilot screw the specified number of turns from the initial settingTOOL Pilot screw wrench
07908-4220201
HIGH ALTITUDE PILOT SCREW OPENING: turn in from initial opening Start the engine and adjustthe idle speed at high altitude to ensure proper high altitude operation